So I started over with my server due to too many issues and a need to get it sorted quickly.
I have pointed mydomain.com to my ip address 111.222.333.444.
When I ping mydomain.com it returns the correct and expected response including the correct ip address.
When I go to mydomain/nextcloud I get “can’t connect to the server” error.
111.222.333.444 is your external IP address?
Port-forwarding on your router is OK?
what happen you enter mydomain.com on your browser?