Your OptiPlex 5090 SFF should have an M.2 slot for NVMe SSD.  It's located at #6 on the motherboard picture below.  No need to contact Dell service to add M.2 socket, technically they can't.   [IMAGE]
I am currently using a 3.5 HDD (7200rpm) without an SSD, and I am interested in upgrading to an NVMe SSD. I noticed that there is an M.2 SSD port near the CPU fan, but it has a non-active label near it and no socket to plugin in. I am facing an issue with Windows updates, which take hours to complete and affect my work. The updates run in the background and take up 100% of disk usage, making it difficult to work. Major updates like Windows 22H took over a day (32 hours to be exact) to update and use my device. I am considering upgrading to an NVMe SSD because it has more write/read speed than a SATA SSD. When I normally reboot my device, it takes 30 minutes to free up 100% disk usage, just to use my system. After this, the system works fine. This issue is causing me a lot of stress, and I am wondering what I should do? I did check the specs sheet. As per this i dont see any option, if i go the dell service, will they add it i mean M.2 SOCKET? How does this work?
Optiplex 5090 SFF, upgrade storage?