So, from another posting (actualy a reply you posted to another embers problem) younhave a 4K display?
Unlike MACOS you can decrease the actual display resolution. In MACOS you can only alter the scaling of the display. Both Windows and MAC have the scaling option. Scaling only makes the display look like a smaller resolution. When you scale, your OS is still using all the pixals
Niw when you actualy change the display resolution, you are decreasing the total number if pixals
Why all that context, I just wrote?
Lightroom, in Develop module recreates each and every pixal to feed to your display. Every time you touch a edit, ir recreates thise pixals.
Lightroom is a parametric application, that us hiw it can be non destructive. as such it recreates each and every pixal, over and over again.
Raster programs like Photoshop, do not do this. They save each edit to temp memoe=ry, and when you add an additional edit, only the pixals modufied get recreated, a lot less work.
So how to fix?
1. If you were extremly lucky, the option to use GPU could help. but apparently not.
2. You will not like this, but, decrease your resolution. In your OS. Lightroom will then create fewer pixals, taje less time. Remember to also decrease your library previews (standard)
Just another Adobe customer; My Sys; APP: LRC 9.4, PS 21.2.1; CMP: WIN WS 16GB OS 10 v1909 (18363), mid 2015 MBPr 15” 16GB MACOS 10.15.6; 4K EXT DSPY; CAM: Canon 5D Mk III, Fuji X-T3