Thank you for this and all the ones that came before.
They keep telling me what wonderful news all this is, and how I should be happy. Maybe they’re right and maybe I will be.
For now it’s wait-and-see mode, fingers crossed that they’ll sort out the migration bugs and holes before ‘support’ for your ‘unsupported’ spin ends: officially or unofficially.
Edit, some hours later: Installed (flawlessly with no updates available) to HDD. I’ll use this partition to test the migration when necessary, before committing to it on my SSD.