While I don't disagree with that, in my experience all Windows instability on WinNT family (and I tightly worked with all end user versions of Win from 16 bit W

While I don't disagree with that, in my experience all Windows instability on WinNT family (and I tightly worked with all end user versions of Win from 16 bit W3.11 to the recent Win11 with a very few exceptions) are caused by faulty hardware and/or bad drivers that can't handle it. I don't think I could remember any issue that I can't attribute to bad HW/3rd party driver. Wrt Win95 & it's kind - all processes in that family essentially run in a single address space, and data "isolation" were "achieved" only through obscurity. If you knew some magic constants that were easily obtainable from disassembly, you could do anything there. So no wonder it was as bad as the worst program you've installed..