I'm yet to meet a toddler who can sit quietly on a bus/train/plane or in a waiting room/cafe for more than 5 minutes!
you should have met MINE then.... He's flown all over the world, up to 11 hours on a plane, eaten in some of the most amazing restaurants and hotels, all without a single device.
I know he is himself amazing, nothing to do with me, but we did chat about things quietly and he just took it all in. Toddlers* don't need devices, they need attention and boundaries. It's perfectly easy to explain that people don't want to hear noises, and in some spaces, they have to be quiet. Yes it's work, it takes an effort but sadly a LOT of parents can't be arsed to take the time or make the effort to show their children how to behave.
Swimming lessons: 2 diabolically posh twitmums sit there braying about crap having sent darlings tristan and jasper along to the other end of the seating area where they take up parent seats and blare their racket. Drives me doolally! it's 30 mins!
*NT, SN the exception as it should be.
Good point though that one SN child's comforting noise could be another SN child's trigger. I dare say that's where compromise comes in.