Unless I am mistaken, the default behaviour for apps in iOS is to remain in a ‘launched’’ state when in the background. ie after opening the app and hitting the device Home button or switching to another app.
Is there a way to make the application quit when it is put in the background?
have you looked in player settings ?
(never used it myself)
since application lifecycle on iOS is completely - and more efficiently - managed by os, there’s in general no need for user, or application itself to interfere with it;
from application point of view background state generally translates to ‘I don’t care’ unless there’s some background processing needed which but seems the exact opposite of what you want