How do I set up a focus mode to prevent certain apps from running on iPhone?

I would like to set up a a mode or a new focus to disabled the app from it ever running.

Example: I am preparing for a hike trip and want to put the phone on airplane mode, and have it only play music and do photos. I don't need Duolingo to remind me Its my last chance.

Essentially stop the apps refreshing at all. Low power mode doesn't seem to do it.

[Re-Titled by Moderator]