This stuff drives me so mad. I recently have noticed higher than usual over-night drain on my phone and decided to investigate a bit. So I connected my phone to my machine, closed out all the apps waited a few seconds and ran adb shell top with a few parameters to see what is actually running.
And would you look at that, despite the phone telling me that nothing is running at all, the microsoft copilot, ebay kleinanzeigen (a german craigslist), google photos and google search either have not been closed or somehow started themselves. Also I have not received any notifications for these Apps in the last few seconds.
First of all, how are these Apps even doing it? With the two Google Apps I kinda get it, since they are System Apps, but in the case of ebay Kleinanzeigen and microsoft copilot it makes 0 sense since they are regular 3rd party Apps. How can they bypass seemingly all optimizations and start themselves (I haven't used the Microsoft copilot app in months). Also is there any way to prevent this from happening or at the very least get some kind of summary how often these Apps ran in the background. Sadly the Android battery information page is totally useless. With many of these Apps I don't care about notifications or anything and I never want them to run after I close them in the task manager.
My samsung S21 has the option to restrict an app and prevent it from ever running in the background, maybe that would do it if your phone has a similar option?