A user, Jonathan5, encountered an issue with posting messages on their iPhone 11 Pro Max when using the desktop view in portrait mode. awesomerobot explained that desktop view isn’t meant for mobile devices, but Jonathan5 pointed out that the desktop-mobile switch on the mobile sidebar can be tempting. Canapin suggested that the issue might be due to the browser being set to desktop view, and Jonathan5 concluded that this might be the case, having occasionally requested desktop mode. They have since switched to the default theme and mobile view.
Continuing the discussion from Searching for a theme - hamburger on left, smaller font:
Using desktop view, default theme, on an iPhone 11 Pro Max on portrait mode, the Reply and Close buttons are almost on screen but not quite, so can’t be used. It’s ok in landscape mode.
You’re not meant to use desktop view on mobile, this is why we have a mobile view
Fair enough. I’d not have planned to. Somehow I got moved to it automatically. After adding it to my home screen and before the forum went into maintenance mode (though probably both coincidences).
But if we are “not meant” to use it, maybe you shouldn’t be tempting us by having the desktop–mobile switch on the mobile sidebar.
Just a guess. If you have configured your mobile browser tab/window to show a desktop view, and you load another website in the same tab/window later, it keeps the desktop view. It happened to and surprised me a few times, but it might also be not your case 
edit: I read a bit fast the last part of your message.
Indeed, I’m not sure why there’s this toggle, especially since most browsers have this feature.
Thanks. Maybe that’s it – sometimes I do request desktop mode. Though I thought the “Add to Home Screen” things used Safari but were somehow separate from it. Default theme and mobile view all the way now!