Adobe audition runs slow on my imac 2020

Check that all the drivers are up to date, especially the video one. I don't know what video device they use in Macs, but people like Nvidia have been known to do almost weekly updates recently, certainly for Windows. From all the comments I've read, and what people have complained about, I get the impression that Apple don't care as much about iMac products as they do about their mobile devices, etc. Suffice it to say that I will not be purchasing anything from them.

The other thing you might want to check out is Mac music optimisation guides, like this one. I suspect that optimisation may be less of an issue with Macs, but it's worth checking that nothing untoward is happening in the background anyway.