Bug on this line: https://github.com/SteeltoeOSS/NetCoreToolTemplates/blob/main/src/Content/NetCoreTool.Template.WebApi/CSharp/Company.WebApplication.CS.csproj#L39
<PackageReference Include="Steeltoe.Connector.ConnectorCore" Condition="'$(Steeltoe3Connector)' == 'True' AND '$(AnyEfCore)' != 'True'" Version="$(SteeltoeVersion)" />
should be
<PackageReference Include="Steeltoe.Connector.ConnectorCore" Condition="'$(Steeltoe3Connector)' == 'True'" Version="$(SteeltoeVersion)" />
The EFCore package depends on the Base connector package but some of the extension methods (eg: AddRabbitMQConnection) are in the Core package