How do I work out if my PCIe is capable of splitting channels on a PCIe slot

I'm currently looking at options to repurpose an older machine (or potentially build a new storage server) in a year or two.

One rather interesting potential piece of hardware is a card that would let me split a x16 port into 4x M.2 bays

The product write up says

Support: Only supports motherboards that can split PCIE channels. Note: Not all motherboards support it, please ask the motherboard manufacturer if it is a motherboard that can split the PCIE channel. advantage:

The price and design indicate this is a purely passive component, but I really don't think that checking with your hardware vendor is always an option. There's clearly no PLX chip,

So practically - how do I check/know that I can split up the channels on an x16 slot into seperate channels, and would system that supported this that have any appropriate bios settings or something else I can look up?