[chrisjc]

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.

https://support.apple.com/en-us/HT202043

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.

[karls]

Nope, I just have an integrated Intel GPU.

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.

¯\_(ツ)_/¯

[chrisjc]

:( 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.