I use BIOS boot selection to dual-boot. MS has broken it twice. I turned off SecureBoot now and just don't run games that require it.
Apparently you can get a mobo with switchable BIOS config (or was it just a switchable SSD?) so the OS didn't even know that there's a second OS around. If there's no connection of the other OS then MS can't break it [as easily]!
IMO it must be malicious, because otherwise it would be caught with remedial testing. I can't believe MS don't include dual boot setups in their testing.
Microsoft got rid of QA years ago. If it was targeted sabotage they could break dual boot setups every single Patch Tuesday. It's just disrespect for users. Like how Copilot and other shovelware such as Candy Crush keep getting reinstalled every few updates, and privacy settings reset every once in a while. Dual booting is likely not even on their radar.