Windows user experience is becoming terrible: new problems like this are popping up every week.

Yesterday I updated the BIOS because a large Lenovo pop-up kept asking me to do so. When I restarted, it told me that PIN login isn't available and I could only log in with password. I tried changing the PIN, but the problem persists, and for some reason the option to completely disable PIN login is greyed out.

Now I can only log in with password, and since 2FA is enabled I need to input a code that I get by email each time I log in. This happens not only when I start the computer, but also when I lock the screen.

I bought this computer brand new 3 months ago...

You need to access your emails, before logging into your computer? What kind of circular dependency is that?