Why? Greta Thunberg doesn't actually do anything. She's just another "influencer". She is all blah, blah, blah. She is a mascot, a show pony, a cartoon.
If you actually want to save the world then you need to do the science and engineering to make it happen.
The world needs better battery chemistries, better solar power, better wind power, better tidal power, better gravity batteries, better thermal storage and distribution, better hydrogen generation. The world needs fusion reactors. The world needs PFAS taken out of the water cycle. And so on.
Media stunts, protests, people gluing themselves to roads and paintings will not deliver practical results.
Only science and engineering will deliver.