If you don't buy an Optiplex with the M.2 SSD option, Dell doesn't solder the slot onto the board so you can never install one after the fact. : r/assholedesign
Optiplex 3040 SFF M.2 - Dell Community
Add NVMe drive to Optiplex 3050 micro - Dell Community
Dell Optiplex 7060-SFF, Core i7-8700 3.2GHz, 32GB RAM, 1TB M.2 NVMe SSD, DVD, Win 10 PRO 64bit, Win 11 Compatible, Grade A Refurbished 1 Year Warranty
M.2 PCIe NVMe SSD HDD Cover Bay WH11F 0WH11F for Dell Optiplex 7070 7090 3090 Ultra
Solved: 7060, M.2 SSD, Windows 10 installation - Dell Community