I couldn’t find anything in Retropie 4.6 beta.
From the 4.6 announcement:
RetroArch updated to v1.8.5.Support for real CD ROM, with the ability to dump the disc image.
I found a YouTube video using Retroarch but it mentions a download folder which I don’t have.
Try looking in \\retropie\configs\all\retroarch\downloads
I also have no cores in Retroarch with which to play the disc.
What disc did you rip ?