why do apps allow more than one queen when pawn reaches the end of the board while in normal boards

It depends on the specific set. Some sets have no extra pieces, but some sets come with an extra Queen or two; the same for pawns. Extra Queens obviously for promotion, but maybe extra pawns because they are small and easier to misplace (and there are more pawns than other pieces). However, over the board or on an app makes no difference; as long as the promotion is legal, then you can always promote to a Queen. Commonly players promoting without an extra physical Queen use a captured Rook to mark a Queen by flipping the Rook upside down as the piece. Theoretically, I suppose anything could take the place of the extra Queen - given that the player indicates what they are promoting into.

p.s. Of course, having too many "odd-pieces" feels like a "skittles chess game."

To set the mind set thats some rare sh1t dont let it happen thats y u get no spares n gotta turn a rook upside down because something should be letting you know that you have a problem and should look at the position again

Thanks for the explanation KeSetoKaiba, I was confused