Skyrim Castle Volkihar Vampirfürst?

I play Skyrim on my Nintendo Switch and wanted to become a vampire prince. I went to Fortress Dusk Watch got a quest, went into the cave liberated Serena and got back a quest. I skipped the dialogues with Serena and came to the castle Volkihar by fast train. I went straight to the gate of the fortress and was to be approached by Serena, but she does not do anything. Without this dialogue, I can't get into the castle. Is this a bug? What can you do about it?

I'm grateful for every answer.

(I've been trying to restart the game and travel fast, complete quests, die and talk to her, everything works, but nothing helps.)

Go back to the cave and see if there's Serena. And talk to her. (But I tell you, being a vampire lord is not fun, I'd rather recommend you werewolf)