We don't often eat in restaurants , but when we do it's usually one of two kinds only.
A reasonably "quality" cafeteria, where we circle the stands choosing our starters and desserts, if any, or cold plates, and then wait at one of three service areas for hot dishes. Then sit at table with food on trays etc. We know most of the selection off by heart by now, and I find less and less to eat there, but my 8 year old son likes it.
The other kind is a really good restaurant, with visiting family or friends , which doesn't happen often, ( five/six times a year perhaps) . We have a favourite one who know us now and remember that my son is coeliac etc. The food is luscious. My son can now read menus, and he has always tended to choose out of the full menu, not just the children's stuff.
So, ( a couple of weeks ago for instance), after a "fruit cocktail", he ate foie gras with layers of spicy honey cake ( a very tiny amount of wheat from time to time is ok) and chopped apple confit and small salad starter, after which tucked into duck breast with raspberry sauce, with tiny potato pancakes and lightly sauteed mixed veg, followed by a selection of cheeses ( blue, goat, creamy, etc), and ... ... icecream for dessert.
He runs around the terrace between courses, looks askance at the resident dogs, plays with his Bionicle or other toy(s) that I remembered to suggest he bring with him. And all goes well.
Restaurants are good. He eats most things. ( other than wheat) I put it down to breastfeeding him for as long as he wanted, ( which as until he was 20 months old ) ; he had time to learn a lot of tastes through my milk, to develop his own taste, connect fully with it, and have confidence in what he puts in his mouth.
He's homeschooled too, so he's used to sitting with adults. And recently he has started joining in with jokes and comments, which still takes me by surprise because for so long he was so "speechless", and because his contributions are so independent, and funny. We don't tend to do that thing, ( and have discouraged it in visitors) , of asking lots of "nice" but deadly dull questions "to show interest", so his joining in is totally spontaneous.