This was the exact same situation I experienced with my old Surface 6. Started to look into Linux firmware on Surface devices and deactivated secure boot because it wouldn't boot Ventoy at all and do nothing, so I figured to try again with no secure boot. It still didn't work so I turned it on again, but was then greeted with this Bitlocker screen which I didn't even know it had activated up until this point. I set up a local account so I had no key to reset or something and was literally not able to do anything besides reinstalling the entire system.
Luckily I had nothing important on it lol
Weirdly the activation was saved on the MS servers so I didn't need to do that again at least (was a preinstalled system so I wouldn't have known the activation key anyways, I thought "When it doesn't work I'll switch to Linux fully because I'm not paying for that garbage system").
After I updated Ventoy I was able to boot again even with secure boot on, there seems to have been an issue with that specific version.
I had Windows on my device since I bought it (around 2018) only upgraded to W11. It never mentioned anything about Bitlocker before this incident so if I had important stuff on it it would have been so over. Well, never save important files on Windows without backup is what I got out of it
This caused me literally bigger problems than my switch to Arch Linux after having only used Windows the entire time xD
Yeah, but it seems we're out of luck