What’s the biggest mystery currently in Genshin?

Here are some contenders:

— What/who is Paimon?

— Who is Hroptatyr?

— Why is Vedrfolnir a crystal?

— Is there a 10th Harbinger?

— What/who are the Heavenly Principles?

— Why did Asmoday attack and trap the Travellers? Where is she now?

— Why is our sibling not a descender/why are they in Irminsul?

— What is the Tsaritsa’s plan?

— Is Dottore actually dead?

— Just how much has been retconned?