Many Thanks, I will try to install. I really dislike Sonoma since it's UI is quite choppy and unstable.Sequoia Beta is doing very well on my 15" 2018 Intel MBP. I suppose, it will work well with your iMac. Only don't leave the Sequoia wallpaper on, as there's an energy problem with that atm. Best change it to another wallpaper. There's an email in the Feedback Assistant from Apple on Sequoia Beta OS. I don't have too many 3rd party apps (Excel, Word, Gimp, Geany, Calibre, VLC and few standby web browsers), and all of them work as they did.
By the way, where can I download the Sequoia pkg or iso file from apple server directly?