On a Debian 10, I was using a mediawiki 1.35.1 with VisualEditor sitting in /var/lib/mediawiki/extensions/VisualEditor.
I installed it using your package (thank you).
Since MW 1.35, VisualEditor is now part of the core extensions, and thus, appears in /usr/share/mediawiki/extensions-core/
After have add the debian backport source and upgraded MW, I see that the old /var/lib/mediawiki/extensions/VisualEditor is still used, making it crash when trying to use (a click on "edit" in a page leads to a "blink" and no more action).
Removing this bare folder and replacing it with the adequate symlink leads to happiness and colorful unicorns.