Which Slot to use?

Unlike mSATA, SSD cards have two types of connectors, also known as sockets: B key sockets and M key sockets A single card can also have both key types

Yes that's the confusion! I read that manual and when I spoke to customer support, they said second slot is also Gen 4 Maybe they are

m2_1 slot 2 expansion card to add an additional Slot to your PC ATX motherboards have ample slots but if you have a small form factor mATX motherboard (usually

m2 slot mainboard Key E normally has PCIe x2, which is not as fast as PCIe x4 for other key types But still Can I attach a standard NVMe SSD to this socket?