E.g., in Germany you get the entire spectrum from “be a professors slave for 6 years with minimum pay” to “I don’t care where you are - but the publications count”.
I wouldn’t rule out the possibility that there are quite a few professors in Europe who would be willing to guide you through (the relatively light weight bureaucracy) PhD process as long as you create and publish high quality research.
Usually a PhD process requires SOME formal training (e.g., attending a fee seminars), peer-reviewed publications and a cumulative summary over your research.
Personally I respect somebody who “freestyled” his way through PhD as measured by research output a lot. E.g., quite a few women take that route along with maternity leaves; which is great because of flexibility without compromise on quality.
I mean, in CS, engineering, physics, there are plenty of areas where you don’t need a lab per se but can just simulate etc. I must admit that depending in the field interaction with fellow PhD students can be super great an valuable (that’s just gonna make life harder for you if you don’t take advantage of it).
Good luck!