I think you may be right about the web. It is not my experience that novices think to look in right-click context menus on the web, with the exception of text operations like copying text that you mention, and sometimes link actions. (I'm basing this off dozens of usability studies on web-based applications, it may be different for older windows applications.)
I have theories -- maybe it's because most web apps do not bother with context menus (outside of text operations), maybe it's because more people have developed their mental model from touchscreen devices where context menus are less commonly used, maybe more people are on laptops with trackpads that do not make right-clicking as obvious, maybe because there's no visual affordance indicating which onscreen elements have a useful context menu and which have the standard webpage context menu so it's a guessing game. I don't honestly know. But I am confident that if you place key functionality in a context menu of a web-based app that most novice users will not discover it on their own. As per Jakob Nielsen: "...be warned: less skilled users rarely use these [context] menus." [1]
Once end-users learn how to use your app (and therefore are no longer novices) then they seem to have no trouble remembering and using context menus, so it's a great way to expose expert affordances.
In the case of my kids I can also say that the Stardew Valley user interface (such as keeping right-click and left-click actions straight) has been the most difficult part of the game so far. And it doesn't seem like it was particularly necessary distinction to make -- there seem to be few cases where both right- and left-click actions are equally appropriate.
[1] https://www.nngroup.com/articles/feature-richness-and-user-e...