Now that Dell 3060 and 3070 Micro MFF have become available quite a bit cheaper than before, please note that both only support M.2 PCIe x2 (though the 3060 documentation indicates x4, the 3070 documentation correctly states x2).
This is a board electronics issue, as the chip-set does support x4.
The M.2 connector however is more versatile than I expected and does support a variety of M.2 keying of which not all “big connector” PCI-e or USB M.2 adapters support:





