Disclaimer: I'm not an Xfce-user
Your screen problem might be related to that new screensaver function:
https://marc.info/?l=openbsd-misc&m=157149480408910&w=2
See also:
https://git.xfce.org/xfce/xfwm4/tree/COMPOSITOR#n114
and the package readme as mentioned in the message on misc@