Word for a redundant, repeated action that has no effect on the outcome of a task

What is the word for something where no matter how many times we repeat an action, it has no bearing on the outcome?

e.g. pressing the 'close doors' button on an elevator repeatedly doesn't make the doors close faster.

e.g. repeatedly clicking the mouse when your computer freezes doesn't help it unfreeze.

Example sentence:

"Repeatedly pressing the 'close doors' button in an elevator is a [insert word here] action"

I'd suggest the word Futile.

According to Cambridge dictionary:

(of actions) having no effect or achieving nothing

"His men made repeated but ultimately futile attempts to retrieve his body from no-man's land."

Synonyms: fruitless, vain, pointless.

An action is idempotent if performing it multiple times has the same effect as performing it just once.

Pressing the 'close doors' button in an elevator is an idempotent action