I can confirm DX12 working 100% after updating to 20.5.1 and installing Windows 10 Update 2004. Significant performance increase from DX11 as well.
DirectX11 works completely fine, but DX12 is bugged with the crashing as others have mentioned. I will continue to use DX11 mode for now. Hopefully next Radeon Driver Update has this fixed.
Same here, with latest Civ 6 updates starting doing it every single load, new game or not, previously it only happened occasionally for me. Disabling High Quality Shader works but wouldn't really want to use that option, you lose ambient occlusion in the process too.
edit: RX 5700 XT w/ Radeon Software 20.4.2, Ryzen 7 3700X + 16GB DDR4-3600 on Asus Prime X570 Pro etc