I have looked at the Path data using the link you asked me to look at.
My D12.3 32 bit IDE has $(PUBLIC)\Documents\Embarcadero\InterBase\redist\InterBase2020\IDE_spoof;$(PATH)
This IDE opens without any problems.
My D12.3 64 bit IDE has
$(PUBLIC)\Documents\Embarcadero\InterBase\redist\InterBase2020\IDE_spoof;$(PATH)
This IDE opens up with the errors in the initial post.
As far as I can see, these paths are identical to the one in the link you provided.
From my experience with smart setup I cannot just uninstall any component from one IDE.
Is it possible to just uninstall these components from the 12.3 64 bit IDE as a short term solution?
Thanks, Simon