Hmm. Why are you using the receiver? I know some folks have had better luck using the Logitech receivers, but on my iMac, I just use an MX Master 3 via Bluetooth and it works fine. Have you tried connecting directly without the receiver? I actually really like the 2020 iMac, but the 2019 is great too. I would actually wait for the apple silicon version if I was in the market, but I think the models you have are great.