Hi! It could be possible, though i'm not completely sure as usually macs refuse to work with macOS versions that are earlier than the version they were shipped with. You can get the installation image and see if it works in paralells or vmware. Let me know how it goes)
2020 iMac is an Intel Mac so I think it should be OK. I've managed to run El Capitan with VMWare Fusion on an iMac Pro with Big Sur. I haven't tried it with Parallels Desktop.