Phones running on Android 11 now has a new feature which suspends cached apps. It exitst in Develooper options and enabled by default on phones which runs on Android 11.
“Freeze apps when cached and unfreeze them once removed from the cache or killed. Frozen apps will not use any CPU cycles, reducing power consumption for misbehaving processes which might attempt to run while cached,” reads the description of the feature on a commit in Android 11’s source code.
If you’re already running Android 11, you can check if the option ‘Suspend execution for cached apps’ is present under Developer options. The toggle seems to be present only on Pixel phones at the moment.