Those in foreign countries usually have to dress up , make advance orders and they don't eat alone
I’m half joking on that. You can eat alone but most others are not. Good restaurants eg with those degustation often need to reserve first, and I suppose it is fine to dress up.
Esp important to reserve in advance for popular ones, dinners and weekends, while weekday lunch not so bad
true advice is if food is deem important in a trip, plan ahead and have a variety of different local cuisine spread out the trip.
avoid red meat and carbs as it is easy to feel full faster: Seafood is a safe option as they tend not to give big portions but of cos these tends to be costly
certain food like paella are served for minimum two pax, then one need to google for exceptions eg some market stores do sell for solo diners though they ain’t as good as the restaurants