Your debug log shows your web interface is using port 8080:
[✓] tcp:0.0.0.0:8080 is in use by pihole-FTL
You can access it using http://192.168.20.42:8080/admin
If you want to access without adding the port, you can reconfigure your Pi-hole to use port 80 running this command:
pihole-FTL --config webserver.port '80o,443os,[::]:80o,[::]:443'