Never mind. Turns out that the screw that Dell included IS the standoff.  It has a large Philips head, and it turns out it also has a tiny hole in the middle that is threaded for a standard M.2 screw. So Dell included the standoff (that looks like a regular screw) but not the mounting screw.  I found one, so I'm good to go and it doesn't look goofy.
I'm setting up a G5 5090 for a friend.  The configuration as ordered from Dell did not include an M.2 SSD, but we ordered one separately to install.  The G5 came with a fastening screw for the M.2 slot area despite not coming with an SSD, so when we received the SSD, I installed it in the slot, but the height of the M.2 connector and the design of the screw means that when fastening the SSD down, it sits at a slant rather than running parallel to the motherboard.  Essentially, the "base" of the SSD that plugs into the M.2 connector is high up, while the "top" of the SSD that gets fastened down is right down against the motherboard because it's screwed down.  The SSD works fine like this, but it just seems a bit odd based on my experience with how M.2 SSDs are mounted in other systems.The Service Manual for this system on support.dell.com shows appears to show a small "post" that's supposed to be under the "top" of the M.2 SSD.  This is not present on this system, although if I had such a post that screwed into the motherboard hole and then presented a second hole on the top into which I could fasten the M.2 screw, that would definitely allow the SSD to sit parallel to the motherboard.  But if a post is meant to be used, then I find it strange that Dell might have included an M.2 screw but not the M.2 post when ordering a system without an M.2 SSD from the factory.  I would have expected either nothing (which would have been irritating) or both the post and the screw.Does anyone here have a G5 5090 with an M.2 SSD that was included in the factory build?  If so, can you check how your M.2 SSD is mounted?
G5 5090 M.2 mounting slanted by design?