I have the UiPathStudio.msi with the 19.4.3 version. When I run the setup, after accepting the terms and conditions the setup does not go to the screen that provides options where I can select to install just the robot and not the studio. The setup skips that options selection screen and directly install Studio and the Robot.
To be honest I believe there is no option to do that.
UiPath Studio and Robot seem to be tied together and that actually has some sense to it - even on production machines you sometimes need to manually open the machine and studio and do some debugging (studio running on a machine with a prod license will actually prompt you that its supposed to be used only for debugging purposes)
If you worry about some users getting an unwanted access to UiPath Studio you can limit or disable the possibility to open it via system settings and the robot will be just fine :).