Could you please clarify if the clipboard worked before? Could you please double-check if there are any programs running that use the clipboard and compete with RU for the clipboard contents? For example, various little utilities like clipboard helpers, touch-typing learning apps, etc.
Please note, that right now the clipboard only allows you to transfer plain text, as the rich content (files, images, etc.) of the clipboard is not synchronized between Viewer and Host yet. However, we already have this in our roadmap and will implement it in our future updates. As a temporary workaround please try using the Drag-n-Drop of files in the Full Control mode or using the File Transfer mode instead
In addition, please note that the RDP mode in Remote Utilities just launches the native Microsoft Remote Desktop Connection client from within Remote Utilities and connects to a remote computer using the RDP protocol.
Finally, in case if you're using the latest 6.12 Beta 2 version of Remote Utilities, please make sure that clipboard transfer is not disabled in the Host settings -> Other tab: