How to tell what kind of M.2 PCIe SSD can be used?

I recently acquired a Dell Optiplex 3050.  The Owner's Manual describes how to install/remove a Solid State Drive (SSD).  It is described as being an M.2 PCIe SSD.  However, that is NOT very specific.  I suspect that this computer was designed long enough ago that the variety of different SSD devices that fit that description may have been much more limited than it is now.  There is something called "Form Factor" that affects the kind of fitting used to physically attach the device to the Motherboard.  I'm also thinking that the Version (e.g., now commonly 3 or 4) may determine whether or not the computer (BIOS) even supports it.  If I want to acquire such a device it is necessary to know more specifics.

From looking at the connector referenced in the Owner's Manual it looks to me like the Form Factor might be 2280 but that is only a guess.  I'd like to be more certain.