How to remove screen lock? I don't know why, but the swipe, and none options have been greyed out.

How to enable them (without factory reset)?

Note: I have unchecked all device administrators (google find my phone, microsoft authenticator etc.), cleared all certificates and restarted my phone. The issue still persists. I don't use any VPN service either.
As far as my knowledge goes, this will happen when you have security credentials or certificates installed, or when another app has administrator access and is preventing you from removing the lock. You can try going into your certificate settings to check if there are any certificates installed and make sure you don't have any apps requiring that you have a lock screen. If I recall correctly, there is a way to see a list of apps using administrator privileges as well. Good luck!