Apple is using a custom connector for the SSD in the new Mac Pro | AppleInsider
Amazon.com: Dataram M.2 2280 256GB PCIe NVMe Gen 3.0 x4 SSD Compatible with Apple MacBook Air (2013-2017) & Pro (2013-2015), Mac Mini (2013) & Pro (2014), iMac (2013-2019) : Electronics