I did the Royal Tea on the Regal back in April 2018 and I know that it was more than $10pp at that time, though I'm not sure what the price is now. We were seated in the Piazza in the elevated booth area and there were about nine of us in my group. Delicious!
In 2019, I attempted to do this again with some friends on the Royal, but we were told there wasn't enough interest from people on the ship to justify holding a session for us to attend. I imagine this would've been much like if not enough people signed up for the ship to do a Chef's Table. Post-restart, I have inquired about doing this again or putting my name on a list to express interest, but I was told that they hadn't started doing it again. Hopefully this has changed!
Of note, the Princess website says the Royal Tea is only held on the Royal, Regal, Enchanted, Sky, and Diamond Princess ships.