You have an M.2 Gen 3 NVMe slot. The maximum speed is around 3600 MB/s depending on the make and model of the M.2 SSD your purchase. If you install a Gen 4 M.2 SSD it will work, they are backward compatible with Gen 3 slots, but it will run at the previously mentioned Gen 3 speeds.
Hi Peeples! I recently purchased a second hand T3620, it comes without any drives or operating system installed and im having a hard time figuring out what type of M.20 NVME drive i can install for best possible performance. I can't seem to find enough information anywhere to find out which version I should purchase. I'm totally confused, I mean, 3 x 4? 4 x 4? 2D? 3D?  If anyone could help me or make a suggestion I'd much appreciate it. Many thanks! 
which drives to install for best possible performance?