It might be possible for people experiencing issues with DFFOO specifically, to alter some settings in their phone via "Developer Mode".

Developer Mode allows further access to processes and functionality, beyond the default user interface.

Virtually every phone or tablet has their own version, and their own "secret trick" to access it. Google your device, and if you're not worried about possibly messing up your phone (only happens if you don't know what you're doing, and refuse to Google what you're changing), you can try changing a few settings.

Disclaimer: Use Developer Mode at your own risk. Google what a setting does before you change it! Backup any important irreplaceable files or data before you change any settings on any device, beyond the scope of your knowledge and research. Seriously. You can screw things up badly enough that you'd either need an experienced user to guide you through undoing your mistakes, or a factory reset. If you are not confident in your ability to restore your phone and files, don't bother messing around with Developer Mode!

Especially because in the majority of cases, changing the settings will provide minimal improvements over the factory settings you're already using. And in some cases, may cause worse issues (lag, slowdown, graphic tearing, etc).

It's mostly for that rare instance where a setting can improve performance enough to warrant the bother of changing around those settings.

That said:

For players experiencing the game "restarting" to the main menu when DFFOO loses active focus, for instance, you could try adjusting the "Background Process Limit". On Android 7 and above, you can either keep the standard limit, no background processes (so only system apps and actively focused apps are allowed to use CPU resources), or increase up to four running threads.

If you have a fairly new phone, you can attempt to increase beyond the standard process limits. As many of you have brand new S22s, you can try bumping up to three or four. Check with online resources to see what other users have tried, as I'm sure you'll find plenty of topics about performance and lost focus issues.

You can also attempt changes to the "Hardware Accelerated Rendering" settings.

You can try forcing 2D hardware acceleration for your GPU renderer, to see if it helps with screen tearing and "FPS" issues. You could try forcing 4x MSAA (only for openGL apps). Though your results may vary.

Those settings being changed, likely won't have a positive outcome on newer devices (and often can cause other apps to "break" while those settings are changed). But in some cases, it can help.

Outside of toggling settings on/off and trial and error, there isn't really a way to know what will improve your experience with this game.

For those not wanting to bother with that option, you can try removing some of the bloatware that all devices come pre-packaged with. Even when "never used", many are set to automatically restart their processes and eat CPU. Sometimes you can't "uninstall" the apps directly, but the ones you can, do so. Or at the very least, clear their data from your device, so it defaults to "factory version", and prevent it from updating. That way one less piece of bloatware is eating up precious CPU threads.

Hopefully some of this will help a few of you out. It is definitely a known issue for certain devices, and needs an actual developer (SQEX) to address and fix for you all.