share folder not listed when creating new SMB/CIFS share

Added a new SSD to OMV 6.9.12-2 based server.

Created a disk, added an EXT4 file system and created a shared folder 'test'

Can't make this folder accessible by SMB.

On creating a new share in SMB/CIFS the shared folder 'test' is not listed in the dropdown box

Any idea whats going wrong and how to fix this?

The problem has been located between display and seat: On my tiny chromebook I didn't manage to activate the slide of the dropdown box ...