Why Biden approved a USD 450-million sustenance package for Pakistan's F-16 fleet?

All the above. Foreign / military policy is chess, not checkers.

And especially it’s not tic-tac-toe as the disgraced traitorous former president seemed to think it was.

Never consider the significance of a move just as a move. Consider it as part of a much larger longer series of moves & countermoves setting up or supporting something really important.