2025-06-26 08:44:18.884 T:1120 debug <general>: CDRMUtils::FindConnector - failed to find connected connector
2025-06-26 08:44:18.884 T:1120 error <general>: CWinSystemGbm::InitWindowSystem - failed to initialize Atomic DRM
The 'van' log continues to show ^ no HDMI device attached. The 'monitor' log is normal in comparison.
If you remove the SD card and power on the board the firmware shows a bios-like screen with information and along the bottom of the screen there is basic detection of EDID data from a connected display device. I'd guess you will see "EDID: none" which confirms there is no display attached (or detected). LE can use either HDMI port for video/audio but CEC only maps to the HDMI port nearest the power socket so you'll see this described as preferred in many forum posts.
The other trick to try, is running "getedid create" when attached to the monitor. This captures the monitor's EDID data to file and configures the kernel DRM layer to read EDID data from file instead of auto-detecting it from cables. This will guarantee the kernel 'sees' a connected device (the monitor) and outputs appropriate to that device. As long as the van HDMI display can handle that input, it might force things to work. If the van display does not like that input, you either need to fix things so HDMI handshaking and auto-detect works, or you need to run "edid delete" to remove the existing capture, then rinse/repeat the process with another HDMI device until you chance upon one that does work. Note that HDMI audio properties are also defined by EDID data, so unless you are using analogue output (or a DAC board) on the RPi the HDMI device you capture EDID data from can be important.