Whoa learned that one at the weekend. Added a new nvme drive, cloned the old drive. I wanted to expand my linux partition, but it was at the start of the drive. So shifted all the windows stuff to the end and grew the Linux partition.

Thought I’d boot into windows to make sure it was okay, just in case (even though I’ve apparently not booted it in 3 years). BSOD. 2-3hrs later it was working again, I’m still not sure what fixed it of I’m honest, I seemed to just rerun the same bootrec commands and repair startup multiple times, but it works now, so yay!