I wonder how did you reinstall iClone. Since you sure it broke after 8.1, you could try to follow the updates history to pinpoint a patch which "misbehave" at your computer.
First uninstall both CC and IC.
Then locate RL download folder within the Hub settings and sort files by date.
Next, install a base release for both IC8 and CC4 (from May 2022) and fully test it for avatar transfer. Note: current avatars may not open in the first release of IC4 and CC8. Try older avatars.
And then install pairs of IC/CC patches and test again until you get the problem back. Then you'd know for sure what patch broke it.
This is how my RL download folder looks like (sorted by date).
I highlighted a base IC/CC release and consecutive patches.

Also, the latest NVIDIA drivers might not always be the best. Couple of years back there was a case where latest drivers cause a huge issue in iClone. Some of us had to go back a couple of NVIDIA driver versions back to overcome it.
There could also be an issue not with iClone but with C++ Redistributables which sometimes reinstalled as you install something else on a PC. Sophus offered a good advise to look at the Application Events Log.
Finally, instead of installing Game drivers (GRD), try installing Studio Drivers (SD).
Hopefully you would finally be able to resolve the issue one way or another....