> The B650 may support it, but not officially.

My guess (having some high-speed design and manufacturing experience) is that the boards were physically designed and qualified around the official spec, which was PCIe 4.0.

Then after some confusion they discovered that the BIOS team had enabled PCIe 5.0 on boards that were never qualified for it. Batch-to-batch variations of the boards could have caused instability because the manufacturing materials and test processes were only targeting PCIe 4.0