Use case: Non-Atlas SRV with per-DB auth.
In this case, the self constructed TXT records do no contain the authSource parameter, but is supplied on the connecting URI.
For Compass, we need to specify this as the authentication database. Compass errors out with an authentication error, and the mongod.log clearly indicates a malformed auth request suggesting Compass is ignoring the authdb when SRV is enabled "UserNotFound: Could not find user user@admin" where admin is not expected.
Additionally, the SRV documentation states:
You can override the options specified in a TXT record by passing the option in the query string. In the following example, the query string has provided an override for the authSource option configured in the TXT record of the DNS entry above.