Check out El burro. Both locations have some dope vegan and vegetarian options but dos in regent Sq. has alcohol and actual seating. Additionally burgatory is a good option when you're meeting up with big time carnivores. They cook an impossible patty pretty much as good as you can and I hear have some good actual meat burgers. MOLA and Subba both have good veggie options but I'm not sure how vegan they are. Subba is most likely pretty vegan friendly). Spak bros has the best vegan pizza and the best seitan in the city (Pear and Pickle used to be best seitan, RIP). Tana (Ethiopian) has amazing veggie options that i believe are almost all vegan. Udipi is a little further out but worth it. Very vegan friendly, amazing authentic Indian. Now for the vegan restaurants, you'll want to check out:

Onion Maiden, duh Zenith (Sunday Brunch preferred) Apteka (100% this is Pittsburghs best restaurant IMO) Shadobeni (so good and at some farmers markets) Kaibur Coffee Plus others that I have yet to visit or try.

Keep an eye out for anything that is a pop up or new spot from the chef of Crumb (pop up vegan burgers) and Viridis (vegan brunch esque Cafe and coffee shop). Viridis unfortunately is no more, but the chef Abbi is one of Pittsburgh's gems.