FWIW I tested a very early 6.1 kernel on my 5 ITX a while back when it started to appear and found that PCIe was not detected (hence no SATA), so I reverted to 5.10, considering that this kernel was still under active development by then.
It might be possible you’d be facing the same problem. If you can issue “lspci -nn”, it would be useful. Maybe 6.1 doesn’t support the 2x2 split for example, I don’t know.