My guess as to why support didn’t mention it would be because support has to cover all Steinberg products, not just Cubase. Then consider Cubase and it’s different version levels, the OS, etc. As you may know, Cubase is a feature-rich deep program used by many different user groups. I would assume support keeps a updated data base, but maybe they didn’t understand your issue the way you finally wrote it here, or the monitor button solution isn’t in the data base and should be added. I certainly agree an email with the standard obvious replies can be frustrating, and perhaps even insulting. However I guess from their end, these obvious replies sometimes provide a solution that could have been discovered from the manual.
These applications are simply too complex to have paid support going beyond the basics. And that’s another problem, support time being wasted by simple questions by users who are too lazy to read.
I learned to stop seeking company support about 20 years ago with Reaktor questions. I discovered that my solutions are often found in forums.