i have installed DietPI buster on a RPi4 with Nextcloud.
Its working fine include lets encrypt to my ddns eg:
https://mustermann.ddns.com/nextcloud
The Server is working fine (with the Port 443),
but now the Port 443 is used from a other Server, i will make a Port switch to Port 4443 eg:
https://mustermann.ddns.com:4443/nextcloud
i cant find: (Sample)
/etc/apache2/sites-available/default
listen 443 ssl; # managed by Cerbot
change to
listen 4443 ssl; # managed by Cerbot
and : (Sample)
/var/www/nextcloud/config/config.php
1 => 'mustermann.ddns.com',
change to
1 => 'mustermann.ddns.com:4443',
and restart the Raspberry Pi
but i cant find the 2 config files.
Can you help me?

(ok for an update of lets encrypt I have to change the port back at short notice, this is known to me)
regards
tux