The following is Celeste Wiki's deadname policy:
DO. NOT. DEADNAME. ANYONE. If someone has just recently come out, please correct any and all mentions of their deadname to their correct name. No mentions of deadnames should occur, even if a person was highly notable, either within or outside of the Celeste community, under their deadname. The only exception is when the user has specifically and explicitly specified that they are fine with being deadnamed.