@OP This Feat might partially be what you want.

Unfortunately, it only provides 2 sorcery points (so you can't use Heighten or Twin a spell level above 2nd) and the sorcery points recharge on long rest, so you can only use one or two metamagic abilities per day. Additionally, this Feat is from a non-PHB source book, so it's unlike to be in BG3.

Your best bet is mods, as changing metamagic to be available to everyone via making spells cost higher spell slots is probably too much of a change (and too niche, tbh) for Larian.