LPT: If your work is blocked by someone else, change the task status to "Waiting on [person] since [date].
You are not blaming anyone. You are making the dependency visible before the deadline becomes your problem.
Edit: This is not for two hours after handing something off. Ask them first, send a reminder, and give them reasonable time for their own priorities.
If you still cannot continue, mark the task as waiting and move on to your next task instead of sitting on it. The point is not to shame anyone. It is to show why the work is paused and keep yourself productive.
And if you are the person blocking someone else, give them the same courtesy. Reply with an update or an expected time instead of leaving them guessing.