Issue resolved - but was a real hassle. Don't recommend this for most users:
1. Completely uninstalled all versions of START
2. Used the "purge" program (https://forums.stardock.com/486022/start10-support-faq#reinstalling) and did full reboot
3. Reviewed and still found folders from START, manually deleted (BTW START11 has a lot of files marked START10...)
4. Checked registry and found entries for START8 .ini files - removed
5. Ran both CCLeaner and Advanced Uninstaller Pro registry cleaners and did full reboot
Win11Pro installation is now moving forward
Bottomline - none of the Stardock uninstallers really "uninstall" and there are a variety of things that may cause Microsoft to believe that an old version of START is still on the system