Update:
had some time and tested again. This time with DP and HDMI extension modules as well as with USB-C and the C-to-C cable mentioned:
- Woke laptop from suspend as usual
- No matter which module, no ouput @ ports 1/2/4
- decided to plug the HDMI module into dGPU USBC port and wake the dGPU → sensors (from lm-sensors) hung, had to hard-reset…
- On first reboot, no module worked
- Power down + reboot: modules were recognized again, but still no output
Here I wanted to try an older 6.5.x kernel.
- since I didn’t install one in my Arch install, I fired up a Fedora 39 live usb (on ventoy)
- Modules were recognized and external displays WORKED! (yes, had two connected)
- checked journalctl and found similar messages as in Arch (+ GNOME finding the monitors)
I then rebooted into Arch with everything still connected and now have working external displays. I also tried the modules in different slots as well as suspend with and without displays connected.
I have no idea why, but it all works now 