I now believe that no one has any perspective at all. In which situations and with which constellations it works or does not work.
There are so many different options:
- Which OS do you come from, which version?
- Where do you want to go, with which version?
I’m now at a point where I can’t say anything more and, above all, can’t recommend anything anymore.
Just my advice, just like @hirnsushi already said: Until there is no and above all tested solution, I would leave the bootloader unlocked.
Lots of discussion, lots of confusion. I myself have no more perspective.