There have been a few screen revisions on the 13, so there's a decent chance that a better screen will be available eventually on the 12 as an upgrade.

Framework 13 is close to 100% sRGB which is important for any kind of creative work or photo editing.

Framework 12 screen is only 66% which is pretty terrible color reproduction. You edit something and it ends up looking like something else on the gold standard consumer devices.