Do you run your laptop on non—native resolution? Or an external monitor with a non-native resolution?
I'm runnign on 2018 MBP, 16GB RAM + 4k external monitor. I experienced the same type of issues a couple of months back — high WindowServer CPU, mega choppy UI after a few days of use. Initially thought it was Safari, but it kept happening with other browsers as well. Researched it a bit and found a thread where someone suggested running both the laptop and the monitor on native resolution. Haven't had any problems since doing that. WindowServer sits at about 10% CPU and ~2GB RAM, current uptime 10 days.
I think I had the same problem as you (similar hw and setup). Do you have a discrete GPU? If so check the link below out. For me, this behavior was due to OSX flip-flopping between discrete and internal GPU. Once I set it to discrete all the time (I'm always plugged in) the problem went away.
Seems to me a different issue than what people are complaining about atm... but what do i know, might be one and the same.
Edit: very weird... Looks like this setting was reverted for me. I just updated from 11.? to 12.0.1, so I wonder if the installer undid some of my changes. No performance issues, but I've literally just my computer on for the first time after the upgrade.
I'm also pretty much always plugged in. It's likely that the issue was manifesting before switching to a 4k monitor, but after switching the issue became unbearable. E.g I'd wait 2-3s to switch between windows or desktops. Running both screens on native resolutions and I'm switching between windows near-instantly.
:( Sorry to hear that... I know it must be so incredibly frustrating!
Sounds like it isn't an issue of flip/flopping between discrete and integrated GPU then... must just be the integrated GPU and its ability to deal with non-native resolutions.
I'm runnign on 2018 MBP, 16GB RAM + 4k external monitor. I experienced the same type of issues a couple of months back — high WindowServer CPU, mega choppy UI after a few days of use. Initially thought it was Safari, but it kept happening with other browsers as well. Researched it a bit and found a thread where someone suggested running both the laptop and the monitor on native resolution. Haven't had any problems since doing that. WindowServer sits at about 10% CPU and ~2GB RAM, current uptime 10 days.