Hm, I spoke to soon. Samsung Game Booster, even if you add apps manually, promptly decides "it's not a game" and "limits services" including the 48Hz mode built into most recent Galaxy phones. I tried it in RetroArch and it's pretty good.
So my problem is UAE4ARM runs too fast, some stuff runs at full 120fps
To fix it, I guess someone could re-upload UAE4ARM and just change the category to Game and Samsung will immediately allow it. It's sad Samsung feels like they can boss users around.
But perhaps there is also a trusted alternative Game Booster where the supported Hz can be enabled for any app. I wouldn't mind it for Youtube either! Anyone have such a suggestion that they've used?