Thanks for updating your signature, Jack. I just assumed that since you switched to PC that you switched to a new PC with Windows 10... Do note that officially, ARCHICAD 21 is considered 'compatible but not tested' on Windows 7.
The last officially fully compatible Windows 7 version of ARCHICAD was version 19:
https://helpcenter.graphisoft.com/technotes/operating-systems/windows-7/
I've not seen any (?) discussion here of people having issues with Win 7 and AC 21 ... but just be aware that it is possible that you may run into something. Good luck with the transition.
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB