Nextcloud by default is looking for a HTTPS connection. You'll need to go into the config and make some changes if you don't plan to use SSL connections. There is a lot of documentation on here, and I know its kind of annoying to dig, but ultimately, you might want to either install a NGINX docker and configure that for Nextcloud, or google Nextcloud http setup and edit the config to allow it to work.
Also, there are a lot of tweaks when it comes to NGINX as well. So if you go that route, make sure you do some digging there. What works for one person won't necessarily work for the next though. Because you are uploading files, things to keep in mind:
Timeouts for file uploads
Authentication
Apps and how they communicate
What you allow into your network
Not sure how much help I was here for you, but I atleast hope I was able to direct you to a better path.