In all honesty, there’s nothing you can do with any VPS (or cloud - AWS, Azure, etc) provider to prevent them from accessing your server as you’re reliant on them to make sure there are no back doors in their images or hardware, and they have a vested interest (maintenance etc) in making sure they have at least some access. But it’s usually rare they do actually log in.
You can tighten up security a little bit by:
Avoiding use of the console and logging out of it when AFK
Checking /etc/passwd and /etc/shadow for passwords for accounts that should be inaccessible, and removing them.
Verifying pam.conf doesn’t provide access to an external authentication system under the VPS operator’s control.
But those three still rely upon there being no back doors embedded deeper into the OS.
In the end, if it’s confidentiality you need, you’re better off setting the VPS up as a proxy to data that’s held on a server you have full control over (ie one that’s in your house), with no secrets kept on the VPS itself. That can be a tough one to set up and is beyond the scope of a simple Lemmy post…