From your text I understand you are not a really tech savvy person and yiu are really struggling with all the service and configuration involved.
If you want a simple tip, stick to tailscale, it is a vpn and will protect all your services because you will not have access from internet. It is pretty safe and the configuration is trivial.
The obvious drawback is that you won’t have internet access without installing the vpn, which depending the use case can be a deal breaker.
Honestly, a proper configured nginx with certificates and strong password are reasonable secure when there is not any misconfiguration. But if you are in doubt stick to tailscale.