Connection problem with RDP by using MacOS RoyalTSX client.
MacOS Big Sur; RoyalTSX 4.3.6 with the RDP plugin of the same version (4.3.6) and upwards is affected.
MacOS Catilina; RoyalTSX version 4.3.6 using RDP plugin 4.2.1 seems to work.
Apple's strict upgrade policy restricts downgrade and newer versions of MacOS and RoyalTSX seems to have issues when connecting through SPS.
Furthermore the RoyalTSX versions had a change somewhere down the line where Apple changed the default OoB configuration of the client.
RoyalTSX configuration by default is actually a protocol violation. It is set with NLA without TLS.
If you change the configuration in the client the connection should pass thourough.