FWIW, I still don't think it's a bad idea to allow being more selective. If just the `Z:` folder was the issue, I would have split that off. But this MR doesn't adress any of the problems Alexandre mentioned:
So why do we need a separate mechanism, with an ad-hoc environment variable? Why is it only usable at prefix creation? Is there a way to unify the features, or make them easier to use? How is it different from `winetricks sandbox`? etc. etc.
If we add `WINEISOLATEHOME` and later decide we want to have `Z:` isolated as well, we'd need `WINEISOLATEROOT` as well, and I'd personally much prefer a WINEISOLATE with options like WINEDEBUG.