The message means you are working with a lookup field (record type).
See this thread for more details.
Then the switch should be modified as below:
Switch(Dropdown.Selected.Value,
"dog",
{ Claims:"i:0#.f|membership|jane.doe@microsoft.com",
Department:"",
DisplayName:"Jane's User Name",
Email:"jane.doe@microsoft.com",
JobTitle:"",
Picture:""},
"cat",
{Claims:"i:0#.f|membership|someone.else@microsoft.com",
Department:"",
DisplayName:"someone's User Name",
Email:"someone.else@microsoft.com",
JobTitle:"",
Picture:""},
{Claims:"i:0#.f|membership|no-owner-default@microsoft.com",
Department:"",
DisplayName:"No-owner-default's User Name",
Email:"no-owner-default@microsoft.com",
JobTitle:"",
Picture:""}
)
Regards,
Michael