Thinkpad X1: I know they need to be single-sided.
Do you think the WD_BLACK SN850X NVMe™ SSD will fit and work on the Lenovo X1 extreme 5th Gen? What other NVMe would? I know they need to be single-sided.
SN850x is a high performance pcie4.0 ssd. Your X1C5 uses only pcie 3.0 wih 4x lanes speed which means maximum of ~3800mbps. If you want reliable storage go with Samsung SSD 980 or 970 Evo Plus. These are great drives that Lenovo uses in their laptops. (PM981a is the oem variant for 970 Evo Plus)
I learn something new every day. So my Laptop cannot run mbps higher than 3800. Was not aware of that. I also found out that at that speed my laptop can run and fit a 4 tb crucial M.2 2280 size drive, at least that's what crucial shows on their website. It gets very confusing to me. By the way my laptop is not a X1C it's a X1 extreme Gen 5, 16 inch screen.