Somehow the EFI partition doesn't mount and it's impossible to troubleshoot via phone, she asked me to put back the old system 😞
I had a colleague at work that had to redo several days of work because of the one drive thing.
The long and short of it is that they noticed that their connection was being super slow, opened up task manager to see if anything was eating bandwidth, saw one drive, went it it, correctly diagnosed that it was uploading files to it and eating up bandwidth, and then deleted all the files in one drive to stop it.
One drive decided that this meant they wanted all the local copies of the files deleted as well. Like, on the one hand, not the correct way to stop that behavior, but also like, the kind of thing a lot of people would try, and it then deleting all the local files in turn is an unintuitive outcome.