> Note, that mentions two x4 or four x4 Gen 3 slots.

That's probably because Raptor so far only tested PCIe gen3 bridge/switch/split cards (if there are even PCIe gen4 ones out already).

> I'm not sure if that means two x4 Gen 4 slots or four x4 Gen 3 slots,
> or if all options are Gen 3.

I guess they mean the latter. Bridging an x8 gen4 slot into two x4 gen4 slots should be possible as well, of course, but someone would have to actually test such card with the board.