Probably the only good mobile games are ports of console/pc games. There are some surprising ports, like the KOTOR games, medieval 2 total war, and lots of square enix's older catalogue. Fortnite, genshin impact, and pubg are probably the biggest games on mobile right now. But yeah nothing really worth going out of your way for, or even bother with at all, if you already have a gaming pc or steam deck.

Maayybee the only real usecase is if you are going backpacking and want to bring some games into the backcountry with you without lugging a steam deck along lol. Digital board games like Root and Wingspan would work well there and have pass around modes if you are with friends. Just remember to bring a battery bank with you, or a portable solar cell.