I have dreams sometimes where i'm in destroyed cities and i'm the only one and I feel very peaceful. What does that mean? Does having social anxiety have anything to do with it?
Social Anxiety could probably be your answer.
Cities could be regarded as something that tries to structure your life, by controlling you through rules, regulations, & confined spaces jam packed with people that usually follow those rules.
We live in a very structured society these days, so in your dream of being inside a destroyed city could mean that you want control of your own life, not be some else's puppet or to be a sheep.
Usually feeling alone could be considered a bad thing, but in your case you welcome it.
It could mean that people in your real life constantly get in your business and disturb your peace. So being alone could just mean that you want some space or "breathing room" for yourself.
I don't see anything bad in your dream, but if you want space or not to be disturbed when performing something personal (Not making a joke!), you might want to let the person who is most likely to disturb you a notice beforehand.
if you have social anxiety and your dreaming of being peaceful in a destroyed city that could just mean you have really bad social anxiety, do you have real bad social anxiety?
since dreams are a visual pun - that makes perfect sense that you would desire a place where you can exist without stress from people