b3 it’s good move?

As a first move for white?

I think Grandmasters can make almost anything playable.

There have been a number of previous forums asking the same question —https://www.chess.com/forum/search?keyword=Nimzovich-Larsen

Nonsense, b3 is a lethal opening, it’s usually a nimzo India pawn structure for white, it’s already effective as black so it’s fine as white. but you would rather not play nf3 immediately because you want to wait for opportunities to play f4. That sets up a strong kingside attack with ne5, rook lift, and bb2 eyeing down the kingside while f4 is blocking the center. Only in specific lines do you play nf3 early but there it’s because black is slow in development and you don’t want to play f4 against g6, but you can still follow-up with ne5 and f4 afterwards in most cases. You would much rather do this than play a reversed qid which is known to be a very drawish structure, not what you want as white

When playing an opening as white which is a reversed version of a black opening, the main question you should ask is how aggressive the line is. I would not play a reversed semi Slav because the semi Slav is a very defensive line where black is focused on trading. The nimzo with f5, in contrast, is one of the most aggressive responses to d4

I don’t think there is any upside to playing b3 before nf3, but there’s probably not too much wrong with starting with b3. You’re just kind of showing your hand right away and giving black more options. I personally like playing the polish opening as a surprise for people I’ve played my usual stuff against, and it can be quite tricky and effective with just a little bit of preparation. Im not a huge fan of hyper modern openings as white myself, but I have a friend that plays a nimzo Larsen type setup almost as a system and tends to do quite well mainly due to his tactical ability and offbeat nature of the opening. He does start with nf3 though rather than b3, I do have to say the engine is not usually a fan of whites position during the opening.

There is an upside, the ability to play f4 as I just explained. Along with numerous other moves. You don’t always just follow-up 2. Nf3 or something.

Very few people have a hand to play against b3.. it’s just a different opening leading to different positions like any opening

It’s not a hyper modem opening either, you don’t cede the center you control e5 via various moves, same way the nimzo Indian controls e4 just with another tempo