Filling in the few fields of an online petition seems like literally the least we can do. But combined with other actions, online petitions can work.
350.org
Ask Anne Marie: How Can I Support the Climate Strikes?

“I want to go to the climate strikes but I have really bad anxiety. What else could I do?”
12 Simple Strategies to Cope with Ecoanxiety

The American Psychological Association defines ecoanxiety as “A chronic fear of environmental doom.” If you have ecoanxiety, try these coping strategies.