Ukraine

Drones are fairly loud, you can hear them unless they are a few hundred feet up if your hearing isn't damaged and there isn't a lot of ambient noise. In this case the drone is tens of feet up, so they could see and hear it.

With how poorly trained and how they are kept in a state of fatigue, the Russians have two options; wait to die and end their misery or run and die tired.

You can see the guy in the background just sitting there waiting for his turn. He isn't shooting at the drone, he is just waiting for one hell to end.

They're cleary aware there's drones above, yes. They seems exhausted, we don't know for how long they're under attack but fatigue plays it's role. They also don't have any counter-measure, and are not trained to act a certain way.

Without good fortifications hiding you from the enemy sight, there's actually not much you can do to protect yourself. At some point it's just every man for himself. You can always give away your mate position, as we can see here, it only works for a brief moment.

I think the guy in the trench was trying to play dead. Doesn't seem to be any cover around, and the drone could easily have followed him if he moved