After some encouragement from commenters on my last post....

​

https://preview.redd.it/td56bojpj1d61.png?width=1920&format=png&auto=webp&s=918a34724b1ba2146e9a5d16a6da34d4980883b3

I managed to get Big Sur running on this build. I will repost the specs for new viewers, but I am now running Opencore as my boot loader, following the Dortania guide for Coffee Lake. Everything functions super well!

Specs:i7-9700k
G.Skill 32GB RAM DDR4-3200
AMD RX580 Graphics Card
1TB NVME SSD
Gigabyte Z390-UD (Rev 1.0) Motherboard, Bios F10j

Thank you to all the commenters on my Catalina install yesterday who encouraged me and pointed me in the right direction for running Big Sur!