Right now this behaves as expected in that we hide preferences that do not apply to the current skin (as Vector doesn't support responsive behaviour). FWIW every skin should probably have its own preference for this to avoid this problem. There are probably use cases for having Monobook not responsive on desktop and Minerva responsive on mobile.

The responsive skin preference is currently defined in MediaWiki core for all skins:
https://gerrit.wikimedia.org/g/mediawiki/core/+/eab7628c59be589c8bba2b29dabd073683778434/includes/preferences/DefaultPreferencesFactory.php#966

No, it does not behave as expected because Minerva is the skin you're going to get no matter the preference. The responsive mode toggle should be accessible so long as MFE is installed.

@Nardog MobileFrontend has nothing to do with this and shouldn't - MobileFrontend doesn't meddle with skins - only content of articles and which skin to display.

This feature was built for Monobook based on feedback from German Wikipedia when responsive Monobook was rolled out by a community member) and upstreamed to core (after feedback from users who didn't like Vector 2022 as responsive). The primary audience (for this preference) is mobile users who use the desktop site. For example, If you view Monobook on your mobile device for example with the box unticked, it will appear very differently.

How this works currently:

• Every skin can define itself as responsive via skin.json. Monobook, Minerva and Timeless are the only skins that are responsive: https://github.com/wikimedia/mediawiki-skins-Timeless/blob/master/skin.json#L22
• The Skin.php class in core will add the viewport tag if the skin is responsive here: https://gerrit.wikimedia.org/g/mediawiki/core/+/eab7628c59be589c8bba2b29dabd073683778434/includes/skins/Skin.php#384
• The isResponsive method checks the preference value and the skin value here: https://gerrit.wikimedia.org/g/mediawiki/core/+/eab7628c59be589c8bba2b29dabd073683778434/includes/skins/Skin.php#367
• The responsive preference exists in core as I've already pointed out in T363674#9753630 and is marked to only display on skins it applies. This was done as part of T291656.

So as far as I can see here the only options I can recommend here are:

1. Reverting the fix for T291656 and always show it with some kind of disclaimer
2. Replacing the preference with a per skin preference rather than a global preference so that the preference only applies to the current selected.

@Jdlrobson If MobileFrontend meddles with "which skin to display" then it absolutely has to do with this. If it gives you Minerva regardless of the skin preference, then why can't it also override the responsive preference? What's the point of a for-mobile site that doesn't have width=device-width anyway?

No adequate explanation given why this can't be addressed in MFE.