I have M2 slot marked as M2X3 What type M2 SSD (SATA, PCIEx

Two types of M2 SSD

2 standard contains variants with up to four PCIe lanes, one SATA 6 Gbs and or one USB port So it is possible to connect PCIe as well as SATA SSDs

nvme m2 ssd slot NVMe has been solely designed for faster media The prime benefit of using NVMe PCIe SSD over any other type of storage is higher output or input operations

nvme slot types An NVMe connection, on the other hand, allows a solid state drive to have its data read straight from a PCI-E slot right on the motherboard