After upgrading from Debian 13 testing to stable (released version 13.0),
external monitors connected via USB-C docks no longer work.

Hardware:
- ThinkPad E15 AMD (Ryzen with Radeon Vega Graphics)
- AMD Renoir [Radeon Vega Series] (PCI ID: 05:00.0)
- Tested with two docks:
  * HP G4 USB-C Dock (1xHDMI Samsung 4K)
  * Thinkpad Thunderbolt 4 Workstation Dock (type 40B0) (2xDP ThinkVision 2K)
- These both docks still work flawlessly with identical Debian 13 KDE Plasma, with Thinkpad X1 Yoga Gen5, i7-10610U & Intel UHD Graphics

Symptoms:
- External monitors not detected (xrandr shows only eDP-1)
- USB-C dock detected but in "Billboard" mode (USB fallback, no DisplayPort)
- No /sys/class/typec/ entries despite typec_ucsi module loaded
- Same docks work with Intel-based ThinkPad X1 Yoga Gen5

What worked:
- External monitors worked correctly during Debian 13 testing phase
- Stopped working after Debian 13 stable release (around one week ago)

What was tried:
- Fresh reinstall of Debian 13 stable - issue persists
- Kernel parameters: usb_storage.quirks, typec.try_role_src=1, amdgpu.dc=0
- Firmware updates (BIOS, dock firmware)
- Both Wayland and X11 sessions

Expected: External monitors should be detected and usable via USB-C docks
Actual: Docks fall back to Billboard mode, no display output

This appears to be a regression between testing and stable release.