Sightings of J-20 at Anshan has persisted for around a year.
According to this CCTV report, J-20 has performed encirclement of an "island". Is it possible that they already flew around Taiwan undetected? The narration happens around the 2:30 mark.
Yes, of course we've had rumours for it for around a year.
I'm just saying that this news report confirming J-20s in NTC is really just a technical "tickbox" for academic purposes -- and doesn't really tell us anything new, while simultaneously displaying just how behind official state media is in confirming things that we've known about like new aircraft deliveries/service.
And I'd be somewhat surprised if J-20s had operated around Taiwan already. Not impossible, but doubtful, for obvious reasons of the relatively new state of J-20 being in PLA service, the relatively limited numbers of J-20s in service, etc.