The ASUS ROG Strix X570-E Gaming only has a Windows 10 audio driver listed and its possible that its not fully featured but with the basics working in Windows 11. I'm leaning on that being the issue.
Realtek goes based on chipset. I have no idea what chipset that it, but its highly probably that Realtek doesn't have an official driver on their website for Windows 11 for that chipset out anyway at this time, if they ever do.
I would just recommend outputting multi-channel audio differently such as through the GPU HDMI, multi-channel outs analog on the back of the board, add-on card, or whatever.
You can wait and see if it ever changes. But, I don't think you're going to find a way to get optical working again with multi-channel without waiting for a small possibility or moving back to Windows 10.
I don't have optical so can't triple check that or whatever. Sound is complicated on computers so maybe you'll find something anyway if you try hard enough :-)