The language of "reality altering", "quantum" etc to me just signals a failure to recognise that RPGing can take forms beyond one fairly narrow playstyle based around the players learning from the GM about the setting and situations the GM has come up with.
This I don't really agree with. Setting aside determinism issues, there are parts of my life where I exercise agency and parts where I don't. Eg I chose my profession - an exercise of agency - but now, at my age and given my experience, am pretty much locked-in - I no longer really have agency over what my profession will be. Within my job, I exercise agency - eg choosing what to research and write on - but also find myself having to do things I wouldn't do if I could choose - I have little agency in respect of those things.
Choosing to play a game is an exercise of agency. In playing the game, I want to enjoy agential experiences. I get enough non-agential experience in other parts of my life. If someone's pitch of a game to me is Just like the rest of your life, in this game you will often find yourself lacking agency, dictated to by circumstances established by other, etc my response is "No thanks!"