Big Sur is disorientingly slow. For example, as I type this message, there is a 1/2 second delay between hitting each key and seeing the letter on the screen. When notifications or windows pop up, they shift size and shape, with the text moving around for 1/2 to 1 second before it settles on a format. I upgraded to solve a compatibility problem with my printer that was introduced in OS 10.15 and it did not fix it. Really sorry I upgraded as it fixed nothing and only brought new problems.