Your phone seems slow or maybe it’s just a habit. You open your recent apps, see all the screens for what’s open, and you aggressively swipe up on every app in the list.
Stop. Don’t do that. It’s okay.
Tldr: You don’t need to manually kill your open apps. It doesn’t slow down your phone. The only time it can be beneficial is if an app is malfunctioning or frozen, it can help to kill it and re-open it. It is often worse for your phone to kill your apps frequently.
Your smartphone is smart enough to manage its own memory. If it is running low on memory, it will start killing apps that haven’t been used recently. Open apps are not slowing your phone down. It can actually slow down your experience if you kill your apps too frequently because your phone has to reboot each app, causing spikes in battery and cpu usage.
Don’t think of that list as “open apps” but as “recently used apps.” Your phone can handle the rest.
By killing apps often, the next time you open it, it has to do a lot more work to open, load data, initialize, etc. So you’ll actually get a slower experience by forcing every app to relaunch more often.
By leaving your apps open, they don’t need to do so much work when you want to use it again.