Has anyone had issues with Topaz ai software that uprezzes standard footage to HD widescreen?

No direct experience but I find this extremely surprising.

Did you get this software from the developer site, and not some dubious place?

Even if installing some software causes instability, you should just uninstall it and it everything should be back to the way it was before. No need to return a Mac because of it. Are you saying you did uninstall and the Mac still was not performing adequately?

Please run Etrecheck and post its full report here. Use the "additional text" button and paste the report into the text box.

Maybe there is still some thing there, or maybe you have other third party software installed that is causing trouble with FCP and others. By looking at the report we may be able to find something, as we often can.

Software can not "kill" your hardware. It can not render hardware "useless." Physically can't happen.

Topaz doesn't do anything at all to damage hardware.

Have you contacted Topaz tech support?

I've been using Topaz Video AI for many years, starring with a 2017 iMac Pro and never had issues.

I thought you were going to complain that it didn't work miracles with your footage.

I have not heard about any of the problems you mention and would suspect there is something about your setup or working conditions that may be to blame . . . though I cannot imagine what.