Debian: HDMI and Notebook Screen work, no Thunderbolt Dock Screen

Hi there,

I’m trying to set up a Thinkpad P73 with two external monitors via a Thunderbolt dock. When connected to the dock, the screens are recognized (xrandr finds them all) but are extremely glitchy - half of the screen is black and the other half is a distorted view of my desktop image with flickering horizontal/vertical lines.

When I connect one of the displays via the laptop’s HDMI port it connects fine. If I connect the second via the dock, it looks glitchy.

Booting the laptop into Windows 10 allows both displays to connect fine via the dock, so I don’t suspect it is problem with the displays, dock, or cables.

I am running Debian 10 and the proprietary Nvidia drivers, with discrete graphics set in the BIOS. (With hybrid graphics none of the external monitors work, only the laptop screen). I am also running GNOME 3.30.2 and gdm3.

Any suggestions for getting the thunderbolt dock-connected displays to not be glitchy?

Thanks a lot!