From the FAQ
"Will there be modding support in Early Access?
Modding will be supported sometime after launch, but not during Early Access. We loved what our modding community did with DOS2, and we’re excited to see what they’ll do with BG3."

We don't know.

BG3 Modder: https://www.nexusmods.com/baldursgate3/users/55895062?tab=user+files