Created attachment 8246
Freez pamac, artifacts, and display through Firefox window.
Created attachment 8247
Looks like an application issue, can you reproduce without the compositor enabled?
Unplugged. Complete unresponsiveness is not present, but slow. Also there is a new bug, hangs DE if you use xfce4-screensaver on the selected area.
V-sync does not work with disabled compositing yet
Hangups are not associated with xfce. Turned out to be a pamac problem.
Actual V-sync and screenshoter
(In reply to Dmitriy from comment #5)
> Hangups are not associated with xfce. Turned out to be a pamac problem.
If not a bug with xfwm4, closing then, thanks.