Identify Floor tiles on the great pyramid of meereen
They are indeed quite beautiful tiles but unfortunately not official LEGO decals.
I believe they are his own original custom designs, as in another MOC for Portal 2 which can be seen at LEGO IDEAS he does confirm that he uses his own custom decals.

I based my design on the amazing 2012 Lego Cuusoo “Thinking with
Portals” by Brickthing. I took his original design and added elements
from Lego Dimensions and my own twist with custom decals and details
from the Portal games.

There seem to be many more examples on that Flickr account.