Any update for you? I've found persistent slowdowns since about the same time. I upgraded my computer at the end of 2021 to help with slow-downs in Fusion specifically and was happy for about 2-3 months. Now it constantly hangs and stalls trying to do fairly basic operations (from my perspective). It is hard to quantify but absolutely feels like the program has gone backwards in recent months.
My system is an AMD 5950X 16-core, 64GBs of RAM, and a NVidia RTX3080, it should be more than enough for the fairly small scale designs I work with. Vertices counts can add up, but Fusion really does not make use of the available resources. It uses a heck of a lot of RAM at times but rarely uses more than 4 of my 16 cores. It is getting really old. I've spent 5 hours today on a design that realistically should have taken less than 1.