For reference, the current standard is PCIe 5.0 which was introduced in 2019 and has since been adopted by the best motherboards with compliance for DDR5 RAM, meaning far superior ...
These include NVMe, PCIe, SATA III, and USB. USB is the most popular for external SSDs, SD cards, and USB flash drives. M.2 slots are used by thin SSDs and can be either SATA III or NVMe (PCIe).