Protesting is basically "doing nothing, loudly." It looks virtuous but has almost zero actual affect on policy. Does any politician actually look at a protest and say "Oh, my, look at that, people don't like what I'm doing! Looks like I have to change my mind."

Not when they’re accompanied with large scale strikes as Europeans have found.

This is status quo propaganda.

Note that I'm not saying you, yourself, are a proponent of the status quo, deliberately spreading propaganda.

But protests are absolutely not useless.

"waaaah they don't change Trump's mind after a single protest waaaaah" of course not. That's not what they're there to do. That's the win condition, not the only move in the game.*

Protests have a variety of important effects, but let's just focus on two of the big ones, which are closely linked:

1) They tell the other people who disagree with what is going on that they are not alone. That there are others like them out there, and that if they do try to do something (whether that's go to a protest themselves, call their congresspeople, or whatever), it won't be just shouting into the void.

2) They tell the people who agree with what is going on that this is not over. They can't just expect to be greeted as liberators; there are people in their own hometown who think that this is not OK, it shouldn't be allowed to continue, and anyone who supports it can expect at least a side-eye at the supermarket, if not much more serious social shunning.

And no: neither of these lead directly to a change in the policies that are being protested. But that doesn't mean that they're useless, any more than it's useless to, say, release wolves into Yellowstone, if what you care about are some of the myriad downstream effects of a trophic cascade.

* Not, I would note very firmly, that it's a game. This is merely a convenient metaphor.