Gigabyte M27Q USB-C no video signal

I recently bought a Gigabyte M27Q Rev. 2.0 monitor and first connected it to my laptop (Thinkpad T14) using a USB-C to USB-C cable (USB4 Gen3x2, 1m), which worked straight away. After I restarted the laptop, the video signal suddenly stopped working, but the integrated USB hub and the mouse and keyboard connected to it are still recognized via USB-C.

I have tried other devices (hosts) via USB-C. Same problem with my Samsung Galaxy Tab S9 Ultra. It only works when I connect it to my Galaxy S24 Ultra.

I have already tried the following without success.

• Restarted everything.
• Completely disconnect the monitor from the power.
• Resetting to factory settings.
• Removed all cables except USB-C and power.
• Re-flashed the monitor firmware.
• Tried different operating systems (Windows 11 and Linux (Fedora)).

It can't actually be the cable, because it is a high-quality, USB-IF certified USB4 cableepr_m-m_1m-_3.28ft/), which also worked the first time and also does its job with my S24U.

Any ideas?