I don't understand which part of releasing patches would not imply it's finished? The campaign is whole, the story is done, the classes are there. There's nothing missing.
My guess is it'll never have an official Linux release. Besides, proton is so good at this point that it will usually outshine a cheap Linux port. In fact, due to the lack of backwards compatibility in Linux land, the Windows edition of a game will typically keep working longer on Linux than the native port. It's a really strange situation.
BG3 was "finished" on release. If it never saw a single update after that, I'd have been happy with it anyway. What they're doing is providing excellent ongoing support to an already solid product.
