wht does the negine say this is not the optimal move?

as above, it seems logical to me? engine 😂

Because the pawn on e4 can take, or the queen can. Why give up a pawn?

It's not letting me post chess diagrams.

The engine thinks d5 is strong because of this line:  1 ... d5  2. exd5  Nb4  3. Qe2+  Qe7  4. Na3  Nxd5 which ends up with you being in a stronger center position than white.  It's not really by much though, compared to other good alternatives like Nf6 or Bc5.  d6 is not a blunder, it's just totally passive.

This leaves black's rook with an open file, and both of black's bishops on open diagonals, while white's pieces haven't really been developed yet. Black also has the option to attack the king by pushing the H pawn up, and could have up to a rook a knight and two bishops pointed at the king.

but with my move it coudn't  thats what i was anticipating, then i take white pawn once he has pushed it and attack queen?

You don't give up a pawn. You temporarily sacrifice one in exchange for better position and getting to capture a pawn later.

Whether d5 is good or not is not the question. Look at the evaluation. White has lost almost a 1 pawn worth in the position. 

So, you have to ask yourself, why do you want to do this on either side? If 2 GMs did this, what would it serve? Just because the engine shows it as the top move doesn't mean you should play like that.

The title is kinda misleading. It doesn't say best, but some may read it that way.

I would prefer to play Nf6.

I let Stockfish 13 chug for a while with infinite depth and it ended up about the same as Nf6 and much less than a pawn down for white.  Different engine settings seem to cause bigger changes than any relative advantage of one of these choices over the other.

If you want to memorize all these knight contortions (on both sides), it's all yours.

[FEN "r1bqkbnr/pppp1ppp/2n5/8/8/3Q4/PPP1PPPP/RNB1KBNR w KQkq - 0 1"]

1.e4 d5 2.exd5 Nb4 3.Qe2+ Qe7 4.Na3 *

thanks, how do i use that info? I assume it's some sort of embedded image or gif?

here it is

The funny thing is people think their opponent will follow along with their memorized lines. 

aye its like, they should not have done that!