Also, the following URLs works:
https://nextcloud.XXXXX.com/index.php/apps/files/
https://nextcloud.XXXXX.com/index.php/login/
So apparently fastCGI only processes index.php and not other PHP files by default? Unless I misread the documentation, it looks like it should use any .php & split on the php. Unless the fact there is an index specified overrides this ability?
From https://caddyserver.com/docs/fastcgi
ext .php
split .php
index index.php