The root cause is that the Android 9 system takes up too much memory. But we can disable some apps not used regularly to free up some pre-installed memory.（I think someone may have sent a similar post before.）
The app in the app list can be disabled theoretically, but some apps don't recommend disabling. Such as TicHealth, because sleep tracking and step counter rely on this app.
I am take the “Flashlight/Torch" app as an example:
Settings -> Apps & notifications -> App info -> System Apps -> Torch -> Disable -> Tick -> Torch -> Force Stop -> Tick -> Enjoy it.