Internal server error when using domain name

for me it definitely sounds as you tamper with the config file of the docker image… don’t you?

take a look at this article it describes Nextcloud Apache Docker image config in fair detail

working apache reverse proxy config (e.g. I don’t see ProxyPassand ProxyPassReverse in your config):

and others Setup Apache reverse proxy with VM

search the forum and read the topics… you’ definitely find a solution.