Does the end step trigger abilities that say 'at the beginning of the next end step' even if it is not your turn?

Triggered abilities that say 'at the beginning of the next end step' are looking for the next end step to occur anywhere in the game, regardless of whose turn it is. The phrase 'next end step' simply means the very next time an end step begins after the effect was created (CR 603.6b, 700.4).

The end step is a phase step that occurs on every player's turn (CR 500.1, 313.1). Once a trigger is set up with 'at the beginning of the next end step,' it will fire at the beginning of the end step of whichever turn comes next — even if that is an opponent's turn.

This matters most when the effect is created during combat or at instant speed during another player's turn. The ability will trigger at the end of that same turn, not wait until your next turn's end step.

Example: It is your opponent's turn and, during their combat phase, you cast a spell that creates an effect saying 'return this creature to its owner's hand at the beginning of the next end step.' That trigger will go on the stack at the beginning of your opponent's end step — the very next end step — not at the end of your next turn.

If you want an effect to occur only at the beginning of your own end step, card text must say 'at the beginning of your next end step' (CR 603.6b). The absence of 'your' makes it apply to any end step.