I came across a small issue regarding the version status of an image that apparently was in OCI format. Unraid wasn't able to get the manifest information file because of wrong headers. As a result, checking for updates showed "Not available" instead. The docker image is the linuxGSM docker container and the fix is really simple.
This is for Unraid version 6.11.5 but it will work even for older versions if you find the corresponding line in that file.