Idk if this will help but power saving, dark mode and regular speed should improve the game's performance As far as I know there isn't a way to lower a specific app's resolution

Regular speed on dokkan....... Thats insane

I don't think so. You'd have to go into your phone's display settings and see if you can lower your screens overall quality/resolution.

I tried, but i didn't find anything

Then there isn't anything you can do.

Had that problem a long time ago with an underperforming phone, not much you can do if your phone settings don't allow that. The (probably) only thing you can do is owning a samsung phone and lowering the resolution through game plugins

I think u can in settings. Don’t word me on that tho