Ah I see. How very weirdly.
I suggest you to try Live11 to see if you can boot Windows 11 from USB live image directly from RAM without install Windows 11.
It is weird. I’m going to try with another 5600x on Friday and if that doesn’t work, I’m certain it’s the board. I’m certain it’s the board anyway. The ram is brand new Kingston 3600 C16, and I’ve tried both sticks individually. I would be amazed if both sticks were somehow faulty, and even then I can’t see why they would cause that with the bios.
I want to install windows 10 on it ideally, as the whole point is it’s for testing loads of old GPU’s I’ve been collecting for a while. Some of them are quite old and don’t have windows 11 drivers.