[out_of_protocol]

There's usually 1 or 2 spots for NVMe drives, but that's it. If you want more, fall back to SATA

[wtallis]

The cheapest motherboard + CPU bundles at Microcenter all include motherboards with three M.2 slots. There definitely are full-size ATX boards that only have two M.2 slots, but these days that's usually only because one of the PCIe slots is wired for x4 rather than just x1. Being able to connect three NVMe drives is not a rare or premium feature on current consumer desktop platforms.

[Longlius]

USB3.2 is almost twice as fast as SATA. If you want extra storage, get a USB-C or thunderbolt external drive.