Same problem popped up for me on a new machine.
GPU accel already disabled.
Old machine was Manjaro (latest, mattermost-desktop 4.4.0, no problem)
New machine, same setup but XFCE instead of KDE desktop
I cant even make use of the webkit debugger console as that one is completely unresponsive as well, stops rendering anything, turns black and crashes mattermost after a minute.
Whenever mm-dektop receives a messages it’s unresponsive for about a minute, barely usable in this state.