There are not all that many ways this could happen, though. I think you can only enter the square of the opposing king with a pawn. With all other pieces, you’d

There are not all that many ways this could happen, though. I think you can only enter the square of the opposing king with a pawn. With all other pieces, you’d have to threaten the square first, which would be check. You could promote a pawn into the king and create a queen on its square. The other way would be if the king itself moves. If the king moves onto a square with an opposing rook and a queen, and decides to capture the rook, the king is trapped until the queen moves. In this scenario, the queen must have moved there in the last turn, putting the king in check. Maybe that’s a new way to get a stalemate.