Should off-screen elements be accessible prior to being toggled?

Reading around the web on accessibility is like trying to comprehend the cloud.

Too much information, too many opinions, too few real world test cases. Which brings me to my question:

Should off-screen/hidden content be rendered in the DOM prior to it being initiated by the user if not relevant prior?

Hiding content, visually, is frowned upon (I say this loosely because it depends), yet in some cases is still necessary; on smaller screens or where the desired expand/collapse/tab functionality is preferred (off-screen menus, etc). If the content being hidden is still viable while hidden, I see a reason for it to be only "visually hidden" yet still remain in the DOM. Now, take for example you have a context menu that pops up on right click, or even a widget for changing font size with a button "change font size" that expands when clicked. Is the content to be displayed necessary from an accessibility standpoint until the user actually interacts with the toggleable element?

I'm speaking in terms of accessibility, not SEO. (or... maybe the two are one and the same these days, who knows, I've been too buried in work to stay up to date).