Yes, I had.
At the moment, I've managed to get it working, but I'm not really sure it's the best thing to do because some other things got removed (a lot of them)... I have a nodejs application that is no longer working, but this is not your problem anymore, haha 
root@ICH-SRV-01:~# apt-cache policy libssl1.1
libssl1.1:
Installed: 1.1.1d-1+ubuntu18.04.1+deb.sury.org+2
Candidate: 1.1.1d-1+ubuntu18.04.1+deb.sury.org+2
Version table:
*** 1.1.1d-1+ubuntu18.04.1+deb.sury.org+2 100
100 /var/lib/dpkg/status
1.1.1-1ubuntu2.1~18.04.4 500
500 http://ro.archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
500 http://ro.archive.ubuntu.com/ubuntu bionic-security/main amd64 Packages
1.1.0g-2ubuntu4 500
500 http://ro.archive.ubuntu.com/ubuntu bionic/main amd64 Packages
root@ICH-SRV-01:~# sudo apt install libssl1.1=1.1.0g-2ubuntu4
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
iputils-arping libbluetooth3 libgudev-1.0-0 libmbim-glib4 libmbim-proxy libmm-glib0 libndp0 libnm0 libpcsclite1 libpython-all-dev libqmi-glib5 libqmi-proxy libteamdctl0 libtorrent19 modemmanager network-manager network-manager-pptp
ppp pptp-linux python-all python-all-dev python-asn1crypto python-cffi-backend python-enum34 python-idna python-ipaddress python-keyrings.alt python-wheel python-xdg usb-modeswitch usb-modeswitch-data wpasupplicant
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
apparmor apparmor-utils apport byobu ca-certificates cloud-guest-utils cloud-init command-not-found curl fail2ban language-selector-common libcurl4 libpython3-stdlib libpython3.6 libpython3.6-minimal libpython3.6-stdlib libssl-dev
libxmlrpc-core-c3 lsb-release netplan.io networkd-dispatcher nodejs nplan openssl pastebinit plymouth-theme-ubuntu-text python-cryptography python-keyring python-pip python-pip-whl python-secretstorage python3 python3-apparmor
python3-apport python3-apt python3-asn1crypto python3-attr python3-automat python3-blinker python3-certifi python3-cffi-backend python3-chardet python3-click python3-colorama python3-commandnotfound python3-configobj
python3-constantly python3-cryptography python3-dbus python3-debconf python3-debian python3-distro-info python3-distupgrade python3-gdbm python3-gi python3-httplib2 python3-hyperlink python3-idna python3-incremental python3-jinja2
python3-json-pointer python3-jsonpatch python3-jsonschema python3-jwt python3-libapparmor python3-markupsafe python3-minimal python3-netifaces python3-newt python3-oauthlib python3-openssl python3-pam python3-pkg-resources
python3-problem-report python3-pyasn1 python3-pyasn1-modules python3-pyinotify python3-requests python3-requests-unixsocket python3-serial python3-service-identity python3-six python3-software-properties python3-systemd
python3-twisted python3-twisted-bin python3-update-manager python3-urllib3 python3-yaml python3-zope.interface python3.6 python3.6-minimal rtorrent snapd software-properties-common sosreport ssh-import-id ubuntu-minimal
ubuntu-release-upgrader-core ubuntu-standard ufw unattended-upgrades update-manager-core update-notifier-common vim
The following packages will be DOWNGRADED:
libssl1.1
0 upgraded, 0 newly installed, 1 downgraded, 105 to remove and 0 not upgraded.
Need to get 1,128 kB of archives.
After this operation, 218 MB disk space will be freed.
Do you want to continue? [Y/n] y
Get:1 http://ro.archive.ubuntu.com/ubuntu bionic/main amd64 libssl1.1 amd64 1.1.0g-2ubuntu4 [1,128 kB]
Fetched 1,128 kB in 1s (1,279 kB/s)
Preconfiguring packages ...
(Reading database ... 88745 files and directories currently installed.)
Removing snapd (2.40+18.04) ...
Removing apparmor-utils (2.12-4ubuntu5.1) ...
Removing apparmor (2.12-4ubuntu5.1) ...
Removing apport (2.20.9-0ubuntu7.9) ...
Removing byobu (5.125-0ubuntu1) ...
Removing python3-apport (2.20.9-0ubuntu7.9) ...
Removing python3-httplib2 (0.11.3-1+ubuntu18.04.1+deb.sury.org+1) ...
Removing nodejs (8.16.2-1nodesource1) ...
dpkg: warning: while removing nodejs, directory '/usr/lib/node_modules' not empty so not removed
Removing cloud-init (19.2-36-g059d049c-0ubuntu2~18.04.1) ...
Removing cloud-guest-utils (0.30-0ubuntu5) ...
Removing command-not-found (18.04.5) ...
Removing curl (7.58.0-2ubuntu3.8) ...
Removing fail2ban (0.10.2-2) ...
Removing ubuntu-standard (1.417.3) ...
Removing language-selector-common (0.188.3) ...
Removing rtorrent (0.9.6-3build1) ...
Removing libxmlrpc-core-c3 (1.33.14-8build1) ...
Removing libcurl4:amd64 (7.58.0-2ubuntu3.8) ...
Removing python3-twisted (17.9.0-2) ...
Removing python3-zope.interface (4.3.2-1+ubuntu18.04.1+certbot+1) ...
Removing python3-configobj (5.0.6-2+ubuntu18.04.1+certbot+1) ...
Removing ubuntu-minimal (1.417.3) ...
Removing nplan (0.98-0ubuntu1~18.04.1) ...
Removing netplan.io (0.98-0ubuntu1~18.04.1) ...
dpkg: warning: while removing netplan.io, directory '/usr/share/netplan/netplan/cli/commands' not empty so not removed
dpkg: warning: while removing netplan.io, directory '/etc/netplan' not empty so not removed
Removing update-notifier-common (3.192.1.7) ...
Removing vim (2:8.0.1453-1ubuntu1.1) ...
update-alternatives: using /usr/bin/vim.tiny to provide /usr/bin/vi (vi) in auto mode
update-alternatives: using /usr/bin/mcview to provide /usr/bin/view (view) in auto mode
update-alternatives: using /usr/bin/vim.tiny to provide /usr/bin/ex (ex) in auto mode
update-alternatives: using /usr/bin/vim.tiny to provide /usr/bin/rview (rview) in auto mode
Removing libpython3.6:amd64 (3.6.8-1~18.04.3) ...
Removing libssl-dev:amd64 (1.1.1d-1+ubuntu18.04.1+deb.sury.org+2) ...
Removing update-manager-core (1:18.04.11.10) ...
dpkg: warning: while removing update-manager-core, directory '/var/lib/update-manager' not empty so not removed
Removing unattended-upgrades (1.1ubuntu1.18.04.11) ...
Removing networkd-dispatcher (1.7-0ubuntu3.3) ...
Removing pastebinit (1.5-2) ...
Removing plymouth-theme-ubuntu-text (0.9.3-1ubuntu7.18.04.2) ...
update-initramfs: deferring update (trigger activated)
Removing python-keyring (10.6.0-1) ...
Removing python-secretstorage (2.3.1-2) ...
Removing python-cryptography (2.1.4-1ubuntu1.3) ...
Removing python-pip (9.0.1-2.3~ubuntu1.18.04.1) ...
Removing python-pip-whl (9.0.1-2.3~ubuntu1.18.04.1) ...
Removing python3-apparmor (2.12-4ubuntu5.1) ...
Removing ubuntu-release-upgrader-core (1:18.04.34) ...
Removing python3-service-identity (16.0.0-2) ...
Removing python3-openssl (17.5.0-1ubuntu1) ...
Removing python3-oauthlib (2.0.6-1) ...
Removing python3-cryptography (2.1.4-1ubuntu1.3) ...
Removing python3-asn1crypto (0.24.0-1) ...
Removing python3-automat (0.6.0-1) ...
Removing python3-attr (17.4.0-2) ...
Removing python3-blinker (1.4+dfsg1-0.1) ...
Removing ssh-import-id (5.7-0ubuntu1.1) ...
Removing python3-requests-unixsocket (0.1.5-3) ...
Removing python3-requests (2.18.4-2ubuntu0.1) ...
Removing python3-certifi (2018.1.18-2) ...
Removing python3-cffi-backend (1.11.5-1) ...
Removing python3-debian (0.1.32) ...
Removing python3-chardet (3.0.4-1) ...
Removing python3-click (6.7-3) ...
Removing python3-colorama (0.3.7-1) ...
Removing python3-commandnotfound (18.04.5) ...
Removing python3-constantly (15.1.0-1) ...
Removing software-properties-common (0.96.24.32.11) ...
Removing python3-dbus (1.2.6-1) ...
Removing python3-debconf (1.5.66ubuntu1) ...
Removing python3-gdbm:amd64 (3.6.8-1~18.04) ...
Removing python3-software-properties (0.96.24.32.11) ...
Removing python3-gi (3.26.1-2ubuntu1) ...
Removing python3-hyperlink (17.3.1-2) ...
Removing python3-idna (2.6-1) ...
Removing python3-incremental (16.10.1-3) ...
Removing python3-jinja2 (2.10-1ubuntu0.18.04.1) ...
Removing python3-jsonpatch (1.19+really1.16-1fakesync1) ...
Removing python3-json-pointer (1.10-1) ...
Removing python3-jsonschema (2.6.0-2) ...
Removing python3-jwt (1.5.3+ds1-1) ...
Removing python3-libapparmor (2.12-4ubuntu5.1) ...
Removing python3-markupsafe (1.0-1build1) ...
Removing python3-netifaces (0.10.4-0.1build4) ...
Removing python3-newt:amd64 (0.52.20-1ubuntu1) ...
Removing python3-pam (0.4.2-13.2ubuntu4) ...
Removing python3-pkg-resources (39.0.1-2) ...
Removing python3-problem-report (2.20.9-0ubuntu7.9) ...
Removing python3-pyasn1-modules (0.2.1-0.2) ...
Removing python3-pyasn1 (0.4.2-3) ...
Removing python3-pyinotify (0.9.6-1) ...
Removing python3-serial (3.4-2) ...
Removing sosreport (3.6-1ubuntu0.18.04.3) ...
Removing python3-urllib3 (1.22-1ubuntu0.18.04.1) ...
Removing python3-six (1.11.0-2) ...
Removing python3-systemd (234-1build1) ...
Removing python3-twisted-bin:amd64 (17.9.0-2) ...
Removing python3-yaml (3.12-1build2) ...
Removing ufw (0.36-0ubuntu0.18.04.1) ...
Removing ca-certificates (20180409) ...
Removing dangling symlinks from /etc/ssl/certs... done.
Removing openssl (1.1.1d-1+ubuntu18.04.1+deb.sury.org+2) ...
Removing python3-distupgrade (1:18.04.34) ...
Removing python3-update-manager (1:18.04.11.10) ...
Removing python3-apt (1.6.4) ...
Removing python3-distro-info (0.18ubuntu0.18.04.1) ...
Removing lsb-release (9.20170808ubuntu1) ...
Removing python3 (3.6.7-1~18.04) ...
Removing libpython3-stdlib:amd64 (3.6.7-1~18.04) ...
Removing python3.6 (3.6.8-1~18.04.3) ...
Removing libpython3.6-stdlib:amd64 (3.6.8-1~18.04.3) ...
Removing python3-minimal (3.6.7-1~18.04) ...
Removing python3.6-minimal (3.6.8-1~18.04.3) ...
Unlinking and removing bytecode for runtime python3.6
Removing libpython3.6-minimal:amd64 (3.6.8-1~18.04.3) ...
dpkg: warning: downgrading libssl1.1:amd64 from 1.1.1d-1+ubuntu18.04.1+deb.sury.org+2 to 1.1.0g-2ubuntu4
(Reading database ... 79708 files and directories currently installed.)
Preparing to unpack .../libssl1.1_1.1.0g-2ubuntu4_amd64.deb ...
Unpacking libssl1.1:amd64 (1.1.0g-2ubuntu4) over (1.1.1d-1+ubuntu18.04.1+deb.sury.org+2) ...
Setting up libssl1.1:amd64 (1.1.0g-2ubuntu4) ...
Processing triggers for dbus (1.12.2-1ubuntu1.1) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for mime-support (3.60ubuntu1) ...
Processing triggers for initramfs-tools (0.130ubuntu3.9) ...
update-initramfs: Generating /boot/initrd.img-4.15.0-66-generic
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Now sudo apt-get --yes --no-install-recommends install lighttpd php-common php-cgi php-sqlite3 was successful and after that I've managed to install Pihole.
PS: I don't recommend the solution above... way to many packages were removed during the downgrade.