plenty vegan friendly restaurants more in the north of mitte (just north of kalkscheune), but unter den linden is a bit of a grey area for non-tourist trap things (surprised the pre-party is there). Nante-Eck is right next to cookies cream, which is an extremely fancy vegetarian place I’ve never been to (tbh, don’t even know if they do vegan).

a while ago I made this list of food recommendations for someone visiting Berlin. Obviously, they all have vegan options https://goo.gl/maps/fzm8PvgNrpFzXkHY6

if the company is paying, I would also recommend Kopps in mitte