What error is this? Is it teling you, the certificate is not trusted?
You can move it to port 80, but you still need to use https, which can be made, but is a very unusual config which is asking for trouble..
Having nextcloud on http is not a good idea, as the traffic is not encrypted. it is (almost) always better to have a https connection even with an untrusted cert (untrusted, but encrypted) than using http (unencrypted and untrusted).
If you start using swag, this will be solved by an official cert issued by letsencrypt.
Ok I'll keep the setup as it is then, thanks.