Error message: "Attempt to write a readonly database"

Got Pi-Hole Blocking to work and Dashboard is showing stats but
I can't save anything parameters in the admin-panel of Pi-Hole:

Changed again file permissions of: "/etc/pihole"

from here:
[Solved] While executing: attempt to write a readonly database error - #4 by deHakkelaar

> 
> root:root      644  /etc/pihole/adlists.list
> root:root      644  /etc/pihole/adlists.list.old
> pihole:pihole  644  /etc/pihole/dhcp.leases
> root:root      644  /etc/pihole/dns-servers.conf
> root:root      644  /etc/pihole/ftlbranch
> root:root      644  /etc/pihole/GitHubVersions
> pihole:pihole  664  /etc/pihole/gravity.db
> root:root      644  /etc/pihole/gravity.list
> root:root      644  /etc/pihole/install.log
> root:root      644  /etc/pihole/list.0.raw.githubusercontent.com.domains
> root:root      644  /etc/pihole/list.1.mirror1.malwaredomains.com.domains
> root:root      644  /etc/pihole/list.2.sysctl.org.domains
> root:root      644  /etc/pihole/list.3.s3.amazonaws.com.domains
> root:root      644  /etc/pihole/list.4.s3.amazonaws.com.domains
> root:root      644  /etc/pihole/list.6.dehakkelaar.nl.domains
> root:root      644  /etc/pihole/list.7.gitlab.com.domains
> root:root      644  /etc/pihole/list.8.blocklist.cyberthreatcoalition.org.domains
> root:root      644  /etc/pihole/localbranches
> root:root      644  /etc/pihole/local.list
> root:root      644  /etc/pihole/localversions
> root:root      644  /etc/pihole/logrotate
> pihole:pihole  644  /etc/pihole/macvendor.db
> root:root      755  /etc/pihole/migration_backup
> pihole:root    664  /etc/pihole/pihole-FTL.conf
> pihole:pihole  644  /etc/pihole/pihole-FTL.db
> root:root      644  /etc/pihole/setupVars.conf
> root:root      644  /etc/pihole/setupVars.conf.update.bak

My:
$ ls -lha /etc/pihole

drwxr-xr-x   3 pihole pihole  12K Mai 26 17:11 .
drwxr-xr-x 146 root   root    16K Mai 25 18:18 ..
-rw-r--r--   1 root   root   5,3K Mai 26 16:21 adlists.list
-rw-r--r--   1 root   root   111K Mai 20 17:08 black.list
-rw-r--r--   1 pihole pihole    0 Mai 26 16:13 dhcp.leases
-rw-r--r--   1 root   root    605 Apr 24 10:10 dns-servers.conf
-rw-r--r--   1 root   root     14 Mai 26 14:01 GitHubVersions
-rw-rw-r--   1 pihole pihole  49M Mai 25 18:13 gravity.db
-rw-r--r--   1 root   root    12M Apr  4 18:02 gravity.list
-rw-r--r--   1 root   root   1,1K Mai 25 12:43 install.log
-rw-r--r--   1 root   root   4,6M Mai 25 13:01 list.0.adblock.mahakala.is.domains
-rw-r--r--   1 root   root   2,0M Mai 25 18:13 list.1.www.dshield.org.domains
-rw-r--r--   1 root   root    31K Mai 25 18:13 list.2.raw.githubusercontent.com.domains
-rw-r--r--   1 root   root    47K Mai 25 18:13 list.3.raw.githubusercontent.com.domains
-rw-r--r--   1 root   root   1,5K Mai 25 18:13 list.4.raw.githubusercontent.com.domains
-rw-r--r--   1 root   root   203K Mai 25 18:13 list.5.raw.githubusercontent.com.domains
-rw-r--r--   1 root   root   143K Mai 25 18:13 list.6.raw.githubusercontent.com.domains
-rw-r--r--   1 root   root   210K Mai 25 12:43 list.7.winhelp2002.mvps.org.domains
-rw-r--r--   1 root   root   1,3M Mai 25 18:13 list.8.www.joewein.net.domains
-rw-r--r--   1 root   root   1,1M Mai 25 18:13 list.9.raw.githubusercontent.com.domains
-rw-r--r--   1 root   root   581K Mai 25 12:43 list.10.mirror1.malwaredomains.com.domains
-rw-r--r--   1 root   root     20 Mai 26 17:10 localbranches
-rw-r--r--   1 root   root     42 Mai 25 18:13 local.list
-rw-r--r--   1 root   root     43 Mai 26 17:10 localversions
-rw-r--r--   1 root   root    234 Mai 25 12:43 logrotate
-rw-r--r--   1 pihole pihole 2,4M Mai 25 12:43 macvendor.db
drwxr-xr-x   2 root   root   4,0K Mai 26 16:53 migration_backup
-rw-rw-r--   1 pihole root    565 Mai 26 15:33 pihole-FTL.conf
-rw-r--r--   1 pihole pihole 233M Jun  4  2019 pihole-FTL.db
-rw-r--r--   1 root   root    708 Mai 26 17:11 setupVars.conf

Error is still present:

While executing adlist_by_group statement: attempt to write a readonly database

Admin-Panel, Stats, DNS + Blocking are Working, but can't save any parameters in the admin-panel.

What's wrong?