I have lots of Blurays ripped to ISO files. Kodi should be able to play Bluray ISO files out of the box. My backend is MariaDB as central dabatase. Sources are mounted via SMB.
In my Windows 18.9 installation I can see each folder in the source I have mounted from the file server and which I have set content as Music video. When I enter each folder, the .ISO is present.
In CoreELEC 9.2.5 when I enter the source, the folders are all there but shown as empty. Since there is no ISO shown, I cannot play it.
I had recently installed the SACD ISO filesystem add-on in the CoreELEC repository in order to test some high def audio ISO files. Worked quite well for me in that I could play back my ISO rips. However, I just noticed today that my DVD ISO rips were not showing (music videos). So, I uninstalled the SACD ISO fs add-on and all my DVD ISOs are now visible and playable. Thanks for the clue in the link to github