Imposter is built for exactly this — no screen-passing required. Everyone answers a question out loud (like "what's your favorite vacation spot?"), except one person secretly gets a slightly different question, and the car has to figure out who. Whoever's navigating just reads the prompts out from one phone.
For quiet stretches, Trivia, the daily Word Guess, and Word Groups hold attention far longer than another round of scrolling. For younger kids, Memory Match, Star Catcher, and Balloon Pop are simple enough to play one-handed.
If everyone in the backseat has their own phone, Four in a Row, Checkers, Chess, Sea Battle, and Dots & Boxes can all be played live, head-to-head — one person creates a game and shares the link, the other joins from right next to them. These are Play Park Pro games.
Open Play Park once while you still have signal — it loads itself onto the phone so it keeps working through the dead zones along the way. "Add to Home Screen" so it's one tap away for the whole trip.