Ho really ? maybe they change it as in the UR interface now.it was not like that few years ago. anyway in UR interface i also found workaround that may work on the new MR installation if u want to try.
i open the UR_extention Dll with notepad in windows,DELETE all its content and save.now the UR Mixer opens even when cubase is running.
(if u are on win10 you may need to move the DLL files to desktop first and delete there in notepad,save and move back to where it was.)