-1

I am looking for few nouns describing "a situation when one does too many things but achieve nothing important or useful".

1

If there's some resource shared between many targets/users in a way that each of them is short on it, you spread [the resource] thin over too many [targets].

In this case You spread your time thin over too many tasks.

1

You're looking for the expression spinning your wheels.

Example: They're on the grind spinning their wheels.

You can also invent your own expressions such as:

Circling around in circles (suggesting no movement or direction inspite of activity)

They're pushing too hard, a door that needs pulling.

Or they're pulling what needs pushing.

They're pushing a brick wall.

They're busy chewing the stones.

They're busy chewing the rocks.

They're taking one step forward and two steps back.

They're trying to fleece leather out of a sheep.

They're working hard counting the hairs on their own heads.

They're making about turns to get there.
0

It may not be exactly what you want, but a word in roughly the same semantic area is counterproductive.

Not the answer you're looking for? Browse other questions tagged or ask your own question.