WindowServer High CPU using external monitor - Big Sur So, few bits of context

I've got a MacBook 12&quot; from 2017
It's connected to an external monitor via USB-C to a Satechi V2 dongle and then HDMI to the monitor

I'm experiencing a few things:

Stuttering when I move windows (like dropping frames)
Videos stutter when my mouse pointer is in motion
WindowServer in Activity Monitor shoots through the roof of CPU usage when I move my mouse a lot
The above is accompanied by the beach ball

See screenshot

I've had a bit of a speedup by disabling &quot;Displays have seperate spaces&quot; in the System Preferences, but it's still happening. It's also slowing down game animations as when my mouse it moving, games won't animate.
Any thoughts?
If you're using an usb mouse, I've noticed that my gaming mouse causes the WindowServer to use a lot of CPU.
Turning transparency down in accessibility settings has helped quite a bit.
As of Dec 9th, 2020, it looks like it's still happening intermittently with one 4K display and my 2019 Macbook Pro.