You can find free rules for the 5th edition pretty much everywhere (it's legal), like here for the ranger class :
https://www.aidedd.org/en/rules/classes/ranger/(french site but you can find all original (EN) content here as well).
It will give you better understanding of underlying base mechanics of this edition, pretty much all of them will translate to BG3 (if the game stay as advertized ofc).
