Unfortunately due to mojangs new drop system the main modpack versions on 1.21.x are right now 1.21.1, 1.21.4, 1.21.5, and 1.21.7 (this will soon be .8)

Of these version the version with the most mods are on 1.21.1 and I am also making a modpack on that version so I would love to see it on that version