If you want to keep your brain wrinkly I'd actually recommend debunking old flat Earth videos. A lot of their arguments can actually be debunked by things you learn in physics class or even maths class around 12 years old so it's not too mentally taxing but still gets those neurons working to do some maths and re-learning stuff about light refraction that's really cool and just generally a ton of SCIENCE.
And as we all know, Science rules.