I have the same exact problem! Everything always worked perfectly with my Roku TV until I updated to the latest AMD driver (20.9.1). I don't know what driver I had previously. But right when I did the update I started to have the same exact audio issue as you. No sound device is detected, and all I get is a red X on the audio icon.
I have tried restarting my computer and TV. Windows Tech Support recommended rolling back to a previous version of the Radeon software, but I don't know how to find what previous version I was using.
@ntaylor6372, can you link the reddit post you made?
Microsoft Windows 10 Home:10.0.19041 Build 19041
AMD Ryzen 3 1200 Quad-Core Processor, 3100 Mhz, 4 Core(s), 4 Logical Processor(s)
Radeon RX 580 Series