Screen Sharing laggy, flickering, and unusable all of a sudden

[brasil]

I've been using Screen Sharing running on a 2012 Macbook Pro to connect to a late 2014 Mac Mini, both running Catalina, with no issues for over a year. The performance has always been snappy with no lag, even with both machines connected to wifi only. All of a sudden about a week ago (and maybe after a Catalina update) Screen Sharing became unusable, with so much lag that it's not even possible to drag windows around, and random flickering to black. No settings changed - it's always been set to adaptive quality and scale to fit. Restarting both computers seemed to fix it very briefly, but it becomes useless again very quickly.

Another issue that seemed to appear at the same time on the Mac Mini (after that same "security" update), and which may be related, is that after the external display was off and the computer in sleep, upon wake up I would find the swap file using 30 GBs of space and the WindowServer process also using huge RAM and CPU. I tried some fixes such as unchecking "separate spaces" for different displays, and checking "reduce transparency," all to no avail.

I was so frustrated with it I updated the mac mini to Monterey since it's the oldest model that's compatible (late 2014). With Monterey I don't see that issue anymore, but Screen Sharing running on the Macbook and viewing the Mac Mini is still useless.

This is driving me nuts. Does anyone have any suggestions? I've googled and searched these forums and can't find anything about this specific issue.

 

[brasil]

Update: I got fed up with it and decided to wipe the whole machine and install a fresh copy of Big Sur. So far all of these issues are gone. Something must have gone bad in Catalina and carried over to Monterey when I upgraded. I would still like to know if I could have fixed the issue without resorting to the "nuclear" option.