The Nikon z8 manual is over 900 pages and will take months to read and absorb. I read a bit in it every day but, "read the manual" is not helpful advice to a complete newbie. We're already reading it and becoming overwhelmed. When someone first gave me that advice, I pointed out that I was trying but that older people can't absorb more than a certain amount of new information in a day, and, even then, we have to go back and review it and work with it several times, or soon it's like we never read it at all. This is brain science. You have to sleep on things to fully consolidate them in long term memory.
So, for me, "read the manual" is lazy advice. While it's understandable that people with lots of knowledge are in a demand and don't have time to do more, it feels like the best way to handle this online is for the busy people not in a mood to chat to ignore the question.
In person, it might be more awkward. "Read the manual" might be better phrased as, , "That will take some time to explain to someone at your level of knowledge, so I can't do it right now." But in a culture where we all strive to be nice and agreeable, this might feel just as awkward to say as "Read the manual," and at least, "RTFM" has fewer syllables so the moment of awkwardness might pass more quickly... So I don't mind if someone says RTM in real life. It's a shortcut...
People who started in film or with a DSLR have no idea how intimidating the manual to an absolute noob. I had to start by learning the names of all the parts of the camera, while you undoubtedly take for granted that everyone knows what a sub command dial is or which is the monitor and which is the viewfinder...