About 207 patches for a new AMD GPU codenamed Sienna CiChlid have been committed to the AMD Radeon Linux Driver. Evidence from these patches suggests that Sienna CiChlid could, in fact, be Navi 21 aka Big Navi. The Sienna CiChlid Linux driver patches confirm support for VCN 3.0 and DCN 3.0 while a leaked slide indicates GDDR6 support and advanced clock and voltage control.
https://www.notebookcheck.net/Fishy-AMD-Sienna-CiChlid-reference-gets-added-to-Linux-driver-patches-likely-to-be-Big-Navi-Navi-21.467635.0.html