What is the best move black can play in this situation?

In this position black should just resign. You can try to prolong the game and hope the opponent blunders, but this position is lost for black unless white blunders.

The exact opposite of this is true. This position is a dead draw unless white knows how to win it. And a low rated player will almost certainly not know how.

White has exactly one winning move now. It would be madness to resign now. Even if white plays the correct Ke4, it's still worth playing a few more moves as it costs nothing.

Well, yes, of course it's  a draw if the opponent makes a mistake, but that isn't how we play chess. We don't just assume that our opponent will play the wrong move. There is no context to this position; we don't know if it is a high rated player or a lower rated player. We can only look at the position and play the game, not the opponent.

By not resigning, you are just prolonging a clearly lost position and wasting both you and your opponent's time which is why resignation is even an option in chess. The cost of not resigning (If the position is clearly lost) is time.

Ok so this is called opposition

there is no best move, white king will simply go onto either side and win through opposition darling as sadly nothing else can be achieved and black will get mated 💕

That is complete nonsense. Ke4 is the only move that wins, all other moves draw.

Quite obviously, he means AFTER Ke4 is played.

indeed

wot