I saw the game Firouzja vs Carlsen in world blitz championship in which Carlsen flagged Firouzja. Carlsen won because even though he had only a bishop, there could be a possible mate position.
I am asking if there a chess position in which both players have at least one piece, not including the kings, and there is no possible future mate position?
An obvious one is if both players having only one bishop moving on the same color squares. But is there something else?
I am actually looking for a complicated position, not obvious to humans at all, which needs something like 30-50 moves deep analysis for proving there is no any possible mate position.