Cover: Folder Images
Keep in mind that the cover display always runs in exclusion order. The sequence is processed from top to bottom. If a cover is found, the process is stopped immediately.
If you prefer the "Folder Images" option, you should drag this variant to the top of the settings.
Finally, save the settings and restart the server.
Cover / Per Song
To add a cover for the song, upload a ".jpg" file with the same name as the music file in the exact same folder.
Cover / Per folder
You can create a cover for a whole folder of music files by uploading a ".jpg" file with the name "folder.jpg" to the respective folder.
Do not simply rename an image file with the extension ".jpg". This will not work! If you don't know how to convert e.g. a PNG file into a JPG file, use search engines to find possible converters.