I agree running multiple AV softwares can be problematic. Maybe try disabling them both as a test? But also just keep one running for real-time. I like Windows Defender and common sense for keeping my system safe.
Did you double check your scratch disk is correctly being referenced in PS? Maybe the drive letter changed during the upgrade but the application still points to an old location?
Also check your Event Viewer System log for errors. Might be some clues in there regarding hardware or OS issues.
Finally, the free benchmark application Novabench might come in handy or provide more info to isolate a bottleneck. It is more general. lightweight, and easier to run than the PS/LR specific ones mentioned above.