I set up openmediavault-s3 today and configured it up to use an existing shared folder.
I then visited the Minio admin page and started configuring access.
Very few of the folders actually appeared in the output of aws s3 ls and I wasn't able to find a way to force Minio to scan my files.
This is because the Minio developers have removed support for existing files since openmediavault-s3 was implemented.
The changes mean that openmediavault-s3 is only a one way link between Minio's S3-compatible API and the shared folder, whereas before it was a two way link.
The changes will also make it awkward if any of the minio metadata gets corrupted and you need to reinstall minio. You then need to re-upload all your data.
I can see why the Minio developers have made this change, but it definitely impacts the usefulness for self-hosters with a single filesystem.