I spent months trying everything I could think of: downgrading to Catalina, turning off transparency/shadows, running as few background services as possible, and not using scaling at all (which was the most effective solution). And this was only with 2x 4K monitors; I added a 3rd more recently.
Nothing worked. Thermal throttling and insufficient sustained power were two problems I was able to identify (the 96W adapter is not sufficient for the system's peak power load, so it uses the battery to get over 96W of draw).
Eventually, I broke down and bought an eGPU (Blackmagic eGPU) which solved the problem. For about ~$700, I'm now able to use my machine without a hiccup. Not a great or affordable solution, but it has made my $3,100 machine usable again.
I’m pretty sure my i9 model has the lower end 5300M.
Another question: what are you using to connect the monitor to your laptop? USB-C to DisplayPort, here. I formerly used HDMI off of a USB-C hub but it was a bummer.
It’s pretty bad the Apple still denies any issue, not being able to use an external monitor at all through covid suuuuucked
I don't "parrot" the claim. I've experienced the problem. It's day and night. After installing Monterey I couldn't run MS Teams on the external monitors anymore. It more or less locked up and I couldn't move the window back to the laptop screen. This was repeatable.
The whole problem went away when I selected 1440p (the "low resolution" one). It's fugly, but at least I can actually use my other monitors.