The same problem here!! After the update to Big Sur my Mac gone So much slower🤯 iMac (Retina 5K, 27-inch, 2017) Processor 3,5 GHz Quad-Core Intel Core i5 memory 40 GB 2400 MHz DDR4 Graphics Radeon Pro 575 4 GB It takes such A LOOOONG time to open and be able to work!! It must be an update coming soon i REALLY want to believe !!

Also I had a problem with safari . I had 2 windows open, my RAM was 35 GB when I start working in a wordpres site and suddenly RAM dropped to 8 and crashed !! I had to force restart my mac !! I wait for the update hoping to correct the issue because I love safari but I don’t use it because of that , instead I use opera , a great browser