Unfortunately, we're still investigating into this feature and whether we'll be able to implement it at some point in our future updates for Mac/Linux. Please note that RDP is a Microsoft-native solution and Remote Utilities has no control over how exactly it functions - the RDP connection mode that you can see in Viewer simply runs Microsoft's own RDP client, nothing more. For now you can see the list of features that definitely will be implemented in the upcoming updates in the very first message of this thread.
I've checked with our developers regarding the RDP feature for Mac and, unfortunately, we won't be able to implement it in our upcoming updates for now. Sorry if this makes our software less useful for you.
Unfortunately, there's no specific ETA on this release for now. However, we will do our best to release the first public beta of Host for Mac/Linux as soon as possible. Sorry that it took longer than expected.