List of steps to reproduce (step by step, including full links if applicable):

• Go to main page on en.wikipedia, logged in
• Click on one of the images, the media viewer should open on the page (url for example https://en.wikipedia.org/wiki/Main_Page#/media/File:Thomas_Luny_-_The_Battle_of_The_Saints.jpg)
• Open the preferences view ("gear" symbol at the right)
• Click "Disable media viewer"
• Close the media viewer
• Click the image again, the file description page opens
• Click "show in media viewer" and go to the preferences view of media viewer
• The preference is still shown as enabled

What happens?:
The media viewer should save the disable option

What should have happened instead?:
The media viewer should kept in disabled mode

I assume the hack linked in the code (T71942) does not longer works as expected.

From my point of view the hack with javascript global wgMediaViewerEnabledByDefault is no longer needed. Just set the default option always, than it would be work for a disabled media viewer as well (this referes to hook handler MultimediaViewerHooks::onUserGetDefaultOptions

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc.: