We're all over the place here.
First off, you have not provided a single error message or warning. For that matter, you've basically provided nothing that really describes what the problem is. We can't help you fix what we can't understand.
Based on your second to last post, and reading between the lines, it sounds like your problem is nothing like what you've described in your first post. If I'm going to take a guess, HTTPS is working just fine. Your problem is that you are getting an unsigned certificate error.
Please try to provide the following: exact steps you are following, what kind of problems you are running in to, and what you've tried to fix the problem. I'll give you an example:
"I'm trying to make sure I'm connecting securely to my Nextcloud over the internet. When I go to https://<ip address>, I get the following warning: 'blah blah blah'. I'm assuming there is a problem with HTTPS. I did a search on Google for "nextcloud https" and found some resources (<insert link>) that I think will solve my problem, but it talks about modifying Apache VirtualHosts Configurations, and that is way over my head. I'm honestly not even sure if I'm on the right path here."