>It says something about 'restart your phone and reauthenticate' that's why I'm asking. What do you autenticate?

You're authenticating that you're the device owner (via your device's saved biometrics or PIN/pattern/password).

>Um yeah but then do I have to install every update via adb? I want to just use F-Droid.

No, once you go through the advanced flow and choose the option to allow installing unregistered apps indefinitely, you can both install and update unregistered apps without going through the flow again (or using ADB).

This part I don't understand. I want to allow for a couple minutes, the time to install a unregistered app, and then go back to deny. I don't want to allow "for 7 days" or "indefinitely". In the text and screenshot of the announcement I see that you can switch these feature "on", but can they be switched "off"?

Ah thanks I'm glad I don't need a Google account to enable this.