I have searched through SAP Help but unfortunately without finding an answer to my question: what defines the autorisation of a certain user to find custom query's in the query browser. I always thought that this is fully dependent upon the standard SAP CDS Views that are being used to build the query.
However, if that's the case, then the next question arises: how can we easily find which business roles contain access to which CDS Views? Now it's quite an extensive job to find out why a certain user cannot find our custom query's in the query browser.