Same thing here, I updated my iMac 2017 from High Sierra to Big Sur and everything went slowwww as a snail. The boot time is terribly slow and I'm seeing frequent spinning wheel when I'm working with Adobe apps such as InDesign as the file name's appearance takes time to load. It's a mistake that I shouldn't upgraded my mac because everything's fine with my High Sierra, and the Big Sur should namely as a Big Mistake. Now I'm thinking of downgrading because I can't work because of the frequent lag. Well, gonna use my Windows PC to continue my work and thinking I'll just erase the Mac's drive and install back the High Sierra again.
Unlike Windows, Apple's frequent OS changes makes their recent Macs obsolete. Thanks Apple!
Osang
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