You’ll need to revert back to V6 SR26 until we figure out what broke.
Uninstall Rhino V6, and reinstall using this link.
http://files.na.mcneel.com/dujour/exe/20200526/rhino_en-us_6.26.20147.06511.exe
Do not update again until we figure this out.
Sorry for the inconvenience.