Windows changed my login and it's SLOW

I started my desktop today (Windows 11 Pro) and instead of the usual enter your PIN screen at login, I was greeted with a "Sign-in to your Microsoft Account." WTH? And because my MS account doesn't have a Passkey associated with it, I had to look up the password on my phone (KeePass) in order to use the silly "Sign in another way" feature. On top of that, it didn't remember the old PIN and I had to create a new PIN. What the heck did Mickeysoft do? I did nothing to change my login. Any ideas? I've also noticed that periodically my computer will slow wayyy down. Rebooting cures it. I have run all manner of scans (offline including from separate boot disk) thinking it might be a virus or rootkit but everything comes up 100% clean. I have no idea if the two issues are related.

Details:

Edition Windows 11 Pro
Version 25H2
Installed on ‎5/‎2/‎2025
OS build 26200.7171
Experience Windows Feature Experience Pack 1000.26100.265.0

Processor    Intel(R) Core(TM) i7-10700F CPU @ 2.90GHz (2.90 GHz)
Installed RAM    32.0 GB (31.9 GB usable)
Device ID    xxx
Product ID    xxx
System type    64-bit operating system, x64-based processor