But nested content that is not nested within other collapsible content appears visually different (the outlines around the entire nested content), no?

As a workaround, is it possible to use a greasemonkey script (browser addon) on Android to make the "m." be removed from the URL when the user agent is set to desktop?

Yes, YouTube. m.youtube.com

Why would someone even want the "desktop mode" to not load the full desktop mode?

In T378193#10262963, @jeremyb-phone wrote:

oops, I think misunderstood which mechanism was being used to get to desktop mode. updated title.

currently the supported way to do this is the mobile or desktop link in the footer of every page.

Ah thanks, sorry for the confusion. I will refrain from using https://en.wikipedia.org/w/index.php?title=Special:Search then, oops

Because it is my browser-synced bookmark for desktop devices, where I want to be able to directly enter an article name/search term without first having to click into the search-field every single time I visit the wikipedia website.

Ok understand.