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Feb 16 19:10:56.709875 LibreELEC kernel: vc4-drm gpu: [drm] *ERROR* Failed to read TMDS config: -121
I've never seen this error on a Pi. It comes from an SCDC command to check scrambling status (something specific to 4kp60 modes).
This uses the I2C pin (also used for reading edid) to communicate with the display.
I'd typically suggest trying with a different hdmi cable, trying a different hdmi input to display, or trying a different display.
But:
QuoteAs of today, I use an RPi4 4GB in an Argon One housing.
Argon cases are widely reported to cause hdmi issues, so first step would be to test without the case.
A workaround would be to avoid 4kp60 modes (4kp30 should be okay).
As most 4k content is 24fps or 30fps this may not lose you much.
Choose 1080p60 as GUI resolution and enable 4kp24 and 4kp30 in the whitelist.