only king remains

'6.9 Except where one of Articles 5.1.1, 5.1.2, 5.2.1, 5.2.2, 5.2.3 applies, if a player does not complete the prescribed number of moves in the allotted time, the game is lost by that player. However, the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.'
https://handbook.fide.com/chapter/E012023

It depends on who runs out of time.
If the player with only the king left runs out of time, it's a loss unless their opponent doesn't have significant material to mate which is a draw
https://support.chess.com/en/articles/8557986-my-opponent-ran-out-of-time-why-was-it-a-draw
If the player with only a king has time left and the opponent runs out of time, it's a draw