Via https://global-search.toolforge.org/?q=wgPopupsReferencePreviews&namespaces=8&title=.*%5C.js we currently see 4 wikis (ruwiki plus 3 others that copied the code by now) that added a Reference Previews killswitch to their ReferenceTooltips gadget because of a mistake that was fixed 4 years ago. This is dead code that doesn't do anything, and should be removed to avoid confusion and possible future issues.
- https://alt.wikipedia.org/wiki/MediaWiki:Gadget-referenceTooltips.js
- https://ce.wikipedia.org/wiki/MediaWiki:Gadget-referenceTooltips.js
- https://inh.wikipedia.org/wiki/MediaWiki:Gadget-referenceTooltips.js
- https://ru.wikipedia.org/wiki/MediaWiki:Gadget-referenceTooltips.js
The original ticket T238991 is a remarkable example for how to not report bugs. It's so badly written, it took us a month to even understand what the problem is.