"Gen 1" vs. "Gen 2" only refers to the P250. There's no such thing as a "Gen 1" vs. "Gen 2" P320, but there is a slight difference between the standard P320 grip modules and X-Series P320 grip modules.
So across the P250 and P320, there are basically 3 styles of mags. (Actually just baseplates; the mag body hasn't changed.)
1) Early Gen 1 P250 mags. These will only work with really early P250 grip modules. You're
extremely unlikely to run across these, unless you're buying used mags off an early P250 adopter who never upgraded his P250. These have a thick floorplate with no "wings" and a slight lip around the front, and have a round retention plug on the bottom.
2) Later Gen 2 P250 and early P320 magazines. These are by far the most common P250 magazines, and were also used for P320s up until mid-2018ish. These have a thinner flat baseplate with two "wings"/"ears" that protrude up from the base, and have a round retention plug in the bottom. These are what came with nearly all P250s. They are compatible with "Gen 2" P250s, as well as with all standard P320s, but won't work the P320 X-Series grip modules without modification or replacement. If you want to get them to work with X-Series grip modules (X-Five, X-Carry, X-Compact, etc.) you'll have to snip off or grind down the two ears, which is easily done. Almost all P250 mags you'll find will be this style, as well as most used P320 mags.
3) Newest P320 magazines, which look similar but have thinner "wings"/"ears", and have a square retention plug in the bottom. These are the newest iterations, introduced a couple years ago. These will work with "Gen 2" P250s, as well as all P320 grip modules, including the X-Series. Nearly all magazines you buy from a store or online shop these days will be this latest style.
(New square plug on top; old round plug on bottom)
Also note that these three different baseplate variations only apply to Full Size and Compact magazines. With Subcompacts specifically, there were no "Gen 1" P250 Subcompacts, nor are there any X-Series P320 Subcompacts. So all P250/P320 Subcompact mags will work in any P250/P320 Subcompact.