bookworm display power management issue

[Scott Lair <scott@lairhome.com>]

Since upgrading to bookworm I'm having a display power management issue. I am using XFCE. Setting the display
power management slider to blank after 5 minutes does indeed blank the display. However, every 30 seconds or 
so the monitor comes back on, then simply displays no signal and goes back off again. This repeats every 
30 seconds or so. I am getting the same behaviour in MATE as well, so it's not unique to XFCE. The machine in
question is an HP Elitedesk 800 G3 with intel graphics. It did not have this issue on debian 11.

Looking for ideas on how to diagnose and fix.

thanks,

Scott