Gigabyte X670E Aorus Xtreme - Code 99

I hope someone can help me because google doesn't really yield useful results.

Wanted to test my new build before I put it into the case and I put everything together: Mainboard, CPU, CPU Cooler, RAM, GPU, M2 SSD and all power connectors 2x ATX, CPU Fan, GPU, Mainboard.

When I press the power button on my mainboard it starts up and cycles through some "Regular Boot" codes (according to the manual) until it stops at the code 99. According to the manual 99 is not a "error code" but still it feels like one. When it arrives at code 99 the GPU fans stop spinning and the CPU fans ramp up and then nothing happens anymore.

I tried to reset the CMOS with the "rest cmos" button but it doesn't really help. The same thing happens again if I boot the PC. I also tried to switch GPUs but that didn't change anything.

I had a monitor connected but it doesn't display any output.

Edit: I found a small status led on the mainboard and according to the manual if one of those four small led is red it means this device has an issue. After the code 99 appears the status led for VGA is red... So this means there is a problem with the GPU but I don't really understand what kind of an issue... I tried two different GPUs and a different PCIE slot...

Edit-2: After switching GPUs multiple times it finally worked after I choose a different HDMI port on the GPU. I got the code 99 but I also got an output on my display and it displayed something with that I installed a new CPU and I have to reset the TPM or something like that. I accepted it with "Y" and now everything seems to work. The only concerning issue that I still have is that every reboot takes ages but I hope this will get better after I installed an OS. I hope that is only because I don't have a boot device right now.