Onkyo TX-SR608 HDMI problems

Hey guys,
as my 2020 Samsung TV is to underdeveloped to play or passthrough any codec other than Dolby Digital, i wanted to connect my PC directly to my AVR via HDMI. Windows directly recognized it as a monitor and audio device with all channels, supported codecs etc., but my TX-SR608 did not.
The HDMI indicator it just blinking and every LED goes black after a few seconds. No sound is playing and the video output just starts glitching or not having signal at all. I already reset it and tried multiple ports and settings.

Do you that i just set it up wrong or is my HDMI Board broken?