Question about Sonero HDMI – HDMI

I no longer achieve 4K 120 Hz 4:4:4. I thought the cable was defective and tried this variant. Without success. Nvidia control panel shows maximum resolution: 'PC: 1360 x 768, 60 Hz, 4:2:0 (HDR works)'. Ultra-HD: 4K 60 Hz 4:2:0 HDR (HDR does not work)'. Does anyone know this problem, that the maximum resolution suddenly no longer works? The following situation: My TV/monitor is the 'LG OLED55CX6LA'. I run the TV either with the old PC (Nvidia GTX 970) or the ASUS ROG Flow X13 laptop connected by the XGMobile RTX 3080. I use this Sonero HDMI 2.1 cable 1.5 m long (48Gbps). For more than a year, everything worked fine with these max settings: TV settings: Game picture mode, HDMI Ultra HD Deep Colour, Instant Game Response, AMD FreeSync Premium (on the Home Dashboard 'PC' is assigned to the HDMI port). PC settings: Nvidia System Control Resolution: PC 4K 3840 x 2160, 120 HZ, Nvidia colour settings set to maximum, HDR, Gsync. For a few weeks now, the 'HDMI Ultra HD Deep Colour' no longer works via RTX 3080. The picture turns black and loses the signal. I only get a picture again when I deactivate it, but then the settings are severely affected. If I deactivate the external RTX 3080 GPU and connect the laptop directly with the internal graphics card (GTX 1650), then 'HDMI Ultra HD Deep Colour' works with the settings of the weaker graphics card, likewise the connection with the PC (GTX 970) works accordingly. Nvidia graphics card drivers and TV drivers are up to date, I have also tested other HDMI connections on the TV. In the meantime, there have been updates to the firmware of the TV and the Nvidia GPU. But nothing has changed. I reset the TV to the factory settings today, but that didn't help either. Can someone please tell me why the RTX 3080 is suddenly no longer compatible with the TV at maximum settings?