You can add domains to the whitelist, but not URL's. If you try to enter a URL, you will receive an error.
From your debug log, you are running Apache, which is an unsupported web server. I have moved this post to the Community Help forum.
*** [ DIAGNOSING ]: Ports in use
*:9090 systemd (IPv6)
[80] is in use by httpd (https://docs.pi-hole.net/main/prerequisites/#ports)
*:443 httpd (IPv6)
*:22 sshd (IPv4)
*:22 sshd (IPv6)
*:3306 mysqld (IPv6)
[80] is in use by httpd (https://docs.pi-hole.net/main/prerequisites/#ports)
*:443 httpd (IPv6)
[80] is in use by httpd (https://docs.pi-hole.net/main/prerequisites/#ports)
*:443 httpd (IPv6)
[80] is in use by httpd (https://docs.pi-hole.net/main/prerequisites/#ports)
*** [ DIAGNOSING ]: Dashboard and block page
[✗] Block page X-Header: X-Header does not match or could not be retrieved.
HTTP/1.1 403 Forbidden
Date: Fri, 20 Nov 2020 18:18:56 GMT
Server: Apache/2.4.46 (Fedora) OpenSSL/1.1.1g
Last-Modified: Thu, 25 Jul 2019 05:18:03 GMT
ETag: "15bc-58e7a8ccdb8c0"
Accept-Ranges: bytes
Content-Length: 5564
Content-Type: text/html; charset=UTF-8
You need to find out under which user apache is running on your system and add it to the group pihole as shown above. Replace www-data accordingly.
See here how to find the right username