We encountered a problem regarding RDP audio input not working in some of our connections.
The Remote Audio device was properly present in session, and browser also asked permission to use microphone, but no audio input stream went through to the recording software. (Also the recording indicator din't appear on browser tab in chrome) Since there was one test machine where audio input worked, we compared the connection profiles. After some testing, we figured out, that RDP "Enable audio input (microphone)" is not working properly when "Disable pasting from client" option is also set in connection settings.
After this, we tested what is the behavior if pasting from client is enabled in connection settings, but in browser the clipboard access is disabled for guacamole site. In this case the audio input still works as expected.