I think we don’t know but in fact I’m quite sure it is NOT yet operational aka officially handed over to the PLAAF … otherwise it would indeed carry a serial number. IMO as it is also rumoured at Weibo a painted prototype during OVEVAL at its future home base.
That is my belief as well.
I think some people are jumping the gun a little bit by using this footage and interpreting it as Y-20B in operational PLAAF service. I think this footage shows a Y-20B prototype in PLA colours doing late stage tests and verification, but not an operational airframe yet