What does the X4 mean in an PCIe Gen X4 NVME drive?

The SSD should work because the _2 slot supports both NVME and SATA but the speed will of cause be lower than the main _1 port Another

All PCIe Generations slots and slots are backward compatible so there is no need to worry about purchasing the wrong expansion card or NVMe SSD But you

m2 pcie slot 4 x PCIe Slots; Full PCI Express Ready Design; Advanced Thermal Solution for PCIe SSD; Easy Software RAID with Single Click to Get

m2 slot mainboard They are all compatible Even a PCIe SSD will work just fine, but the speed will be limited to PCIe x4