How can I access which containers uses which overlays without using docker CLI.

[tchaton]

I would like to be able by checking the files directly.

[polarathene]

If you want to inspect the image content, a TUI like dive is good for that. At run-time Docker Desktop GUI also works well for containers.

If you're not interested in image content or container run-time state, but files you're wanting to persist, use a bind mount volume and you can inspect content locally through your file browser?