Block internet on a Windows 10 computer / unblock it with a password

I’d like to block internet by default on a Windows 10 computer (connected with ethernet cable).

Temporarily, I’d like to allow internet access (by launching a script .bat, .py (Python is ok), or anything else), with a password prompt.

After a reboot, it should always return to “blocked”.

How to do this with Windows built-in tools (ideally without installing any third-party software)?