Roons default method is to first get artwork and extra data from its metadata services. It first needs to match the album to one in its sources, this relies on ensuring your naming and metadata to be correct in the files and folders.
If for a reason the album metadata can’t be matched because it’s wrong or it’s just not in Roons metadatas services then Roon will mark the album as unidentified and you won’t get any extra metadata or artwork and it will fall to using embedded artwork.
Check to see if it’s unidentified first and see if you can manually identify to get a match. Select the album in question and using the 3 dots menu choose edit and proceed to identify it. If it still fails to still identify it then you can choose artwork yourself from the file or load in an image file . Not sure it looks for separate artwork files in the folders only emebedded artwork but I think they should be labelled as cover.jpg or folder.jpg this is what most apps expect to look for not album.jpg. If you only have a separate file then you can manually add this to the album in the edit menu. I have had to do this for a few rare albums not in its services.