Can someone explain this puzzle?

not an easy one but I guess b5 followed by b4 and black opens the Queenside and is a bit better

Black is going to open the queenside (and has two rooks on open file) and there is nothing white can do to prevent that because pushing the b pawn will result again in the queenside opening.
A sneaky puzzle for sure

I solved it in one is B5 followed by B4

Another one that definitely puts the "puzzle" in Puzzle...

White just added a new attacker to b5, and neither player noticed that that didn't prevent b5 because that square has three attackers and three defenders. Neither player noticed that the queen needed to remain where she was to prevent b4 after b5.

1) The rook on b8
2) The bishop on c6
3) The queen that can move to b7. Whatever piece black captures with will be pinned after Qb7. It can't move without allowing Qxb2+.

Looks like a pawn push to me, but I am not a specialist.

the reason why it works / is good is sooo far down the road its frankly ridiculous. puzzle starts at move 16, 7 moves later the computer creates a passer, now it sacs a B at move 24 that gets compensated back 10 moves later on move 34! on move 39 the passer eventually promotes and its a Q vs B endgame (depth 21-23).

i dont think that even 1% of people on lichess could calculate the 7 moves up to the passer within 1 hour, its simply too deep and not forcing enough. allot more players could get to the position when they play vs computer move by move ofc.

btw the puzzle is down 100 rating already since this thread started coz there is some bug it seems. normally if you navigate to puzzles from forum via hyperlink they are unrated.