They are vegan, they get involved at their school on environmental improvements, they make sure they don't waste etc. and they make sure to highlight the plight of the future to others.
I honestly don't know how you can look at Greta Thunberg and underestimate the impact she's had on public discourse on climate change.
In before trolls have a go at them for being vegan, this very respected recent meta analysis published in science clearly finds that going vegan is the number one thing you can do to help most climate change factors https://josephpoore.com/Science%20360%206392%20987%20-%20Accepted%20Manuscript.pdf
You have never seen any impact because you're trying to mash your hands over your ears and close your eyes. I literally just told you the an impact she's had on my family and you still don't recognise an impact.
Of course, I'm sure anecdotes mean nothing to you, so look further at the awards, media attention, speeches, international demonstrations that started with her. Zero impact? Jesus, we are having this conversation because of her.
Honestly, if you can't imagine that this particular household name, face of Time magazine and organiser of global protests has had any impact at all, you probably also believe that the moon landing was faked, the election was stolen, the earth is flat, and there's no helping your unhealthy relationship with bad takes.