Lightroom performance is TERRIBLE after upgrade to Big Sur

I did run AM for all processes. Without running Lightroom 5.4GB out of 16GB is being used. Running Lightroom jumps it to 8GB. The next largest item is WindowServer, which is consuming 0.4 GB. Adobe says Lightroom is compatible with Big Sur, but there's obviously a problem. Any other thoughts?

Yes, they're ordered by CPU%. Given no competing processes, does that suggest a software conflict between LR and Big Sur? As I said, all was working reasonably well on Catalina. The slow down started when Big Sur entered the picture.

Good news first: A workaround has been found from Adobe's user forum. I dropped from LR 10.1 to 10.0 and the problem went away. To answer your other questions: 1.) Yes, LR 10.1was causing plenty of strain on both CPU and memory. I checked after the downgrade and the impact was much lower. 2.) Yes, I tried Safe Mode and saw no improvement. 3.) Regarding something interfering with the Mac, I suspect more specifically with the 27" retina display since it didn't happen on the MacBook Pro. 4.) Mouth and Trackpad were both Apple and both Bluetooth.

Lastly, I'll say thanks Halliday for the effort and staying with me. It was a great contribution toward getting me back to work, which is what I'm going to do now. We can close this string.

It's a Fusion drive that has both the apps and lots of (too many) data files on it. I'm in the process of shifting to a configuration that will move the "heavy" data (mainly photos and movies) to external drives. The HD in the Mac will be used to run the computer. External drives will still spin because SSDs still aren't available in the sizes I need. 8TB and 28TB RAIDs are being installed next week.

All this is to hopefully keep the iMac running until Apple silicon is deployed on the higher end machines.

Thanks again.

16GB for now. Not buying more for now. I think it will run fine once I get this data off the HD that's used by the OS & apps.