Here’s a sneaky trick your friend probably hasn’t told you. Instead of closing apps, you can stop them from updating in the background. Go to Settings > General > Background App Refresh. It’s like putting your apps in a quiet time-out corner.
You can turn it off entirely, or pick specific apps. For example, keep Instagram refreshing (so your feed is fresh) but turn off that random puzzle game you haven’t opened since 2019. This saves massive battery without closing anything.