what value to return at ply >=maxply ?

[MahmoudUthman]

stockfish returns the evaluation value unless incheck it return a draw value , why is that ?

[cdani]

stockfish returns the evaluation value unless incheck it return a draw value , why is that ?

Evaluation due to the inability to go further, so the does the same done at the end of quiesce, and draw value for check due to inability to evaluate at all. For this second case also could had been used the static evaluation of the previous ply, just to return something. In any case the effect of this is 0.

[hgm]

It should not matter because it is not supposed to happen on a branch that makes sense.