I went with the FLIRC passive cooling case https://thepihut.com/collections/raspberry-pi-cases/products/flirc-raspberry-pi-4-case

I'm on Ubuntu 20.04 and I cant find a way to measure temperature at full load right now from the CLI, but I think that case does a pretty good job of passive cooling. I have it sitting on my steel 24" screen arm base too, which is pretty chunky and probably adds a lot of heat-sink.