I have the latest LR 7.3. I recently upgraded my system from 32GB to 64GB or RAM. I have a Ryzen 1800x CPU and a GTX1080 (8GB). I STILL have massive lag at times, with nothing else running on my system. Last week it was so bad that I finally quit and rebooted. Adobe had promised HUGE performance increase -- I've yet to see them. It's a modicum better with 64GB or RAM, but nothing to write home about.
As I mentioned in an earlier post, Adobe has even said "don't do a lot of adjustments". If you do adjustment brushes, they are supposed to be done BEFORE doing global adjustments etc. Of course, I don't know what I want to do as a local brush until I see what I do overall. Counter intuitive.
The one area that has been improved significantly is the auto-mask function. It used to be that you'd get these funky/grainy edges (let's say when softening skin) where the mask was applied. Very noticeable. That seems to have been rectified.