I have the same issue with BigSure 11.4 (and earlier versions of BigSur). I installed BigSure fresh on a MacBook Pro (15-inch 2019) 2,3GHz 8-Core Intel Core-9 32GB memory Radeon Pro 560X 4GB I have an externan Monitor (Dell U3415W) Previously i connected it via HDMI and an adapter but since a month ago I use a Belkin Thunderbolt-3 Dock Pro where the external monitor is connected through DisplayPort. The problem exists before I changed to the docking station but maybe is a little more frequent now. It is not unusual that it is either Microsoft Outlook or Microsoft Teams that are the app that stop working first but there are others as well. I mostly work with IntelliJ or Visual Code with both Teams and Slack running. Also use Mail and Safari a lot. For anti virus I use Avira (only AntiVirus Pro). I also get screen freezes from time to time that seems to be shorter than the time out so I usually just wait (frustrating) till it unfreezes and can then continue to work. When I check the Activity Monitor after the freeze the Window Server is usually pretty busy. Apparently something is bothering the Window Server but the question is what. Before BigSure this happened maybe on or two times per year now its several times per week. Please Apple, fix this!