When you dig through driver code for AMD Radeon graphics that ships with Apple's MacOS "Big Sur" developer beta 1,you'll notice an entry called AMD NAVI31 GPU. 

Rogame, who started his website Hardware Leaks noticed exactly that.  It is the first mention of a chip called like that. Of course there is Navi 21, the RDNA 2 chip which we think could be 'Big Navi', so Navi 31 seems to be a future Navi chip with perhaps RDNA 3 architecture. Radeon Instinct MI100 and MI200 also are listed. AMD's chief technology officer officially mentioned earlier on that MI100 should be released sometime in the second half of this year, MI200 is a mystery though. 

Furthermore, it can be seen that support should be provided for Cézanne and Van Gogh chips from AMD. These are APUs ,  processors with an IGP. Never have we seen Apple make products with AMD CPUs. It's in the code alright.

Apple MacOS Big Sur Beta Driver Code Hints towards AMD Navi 31 GPU and APUs