Can I leave AirPods charging over night?

Don’t concern yourself with it. iPhones have optimised battery charging, and according to recent Twitter posts I’ve seen, AirPods do too now. Once they learn from you’ll habits, they’ll start delaying charging until later etc. to increase the lifespan of the battery. Ideally don’t let them run below 20%. The AirPods Pro and any true wireless headphones have tiny built in batteries, so unfortunately they will only last a few years due to the technological limitations of Lithium Ion batteries. Just enjoy using your devices in the moment.