On English WP, the hover cards / link previews / popups which appear when a logged-out user hovers over an internal link come with a 'gear' icon which can be used to disable them; to disable the disabling, or re-enable, them, one is told to click on a link in the footer of the page "Enable previews". Clicking on it does nothing. The previews remain disabled, with only standard HTML tooltips appearing.

I have tested this in Firefox (85.0b3) & Chromium (87.0.4280.66) on Ubuntu Linux (18.04.5) with my standard profiles & --temp-profile, and others have tested this on Mac with Chromium. Hard-refresh & clicking does nothing. There are no console debug errors or warnings that appear relevant. There appears to be no way to re-enable previews short of using a new profile or dumping cookies.

I have briefly tested it on some other Wikipedias like German & Japanese & test2 (1.36.0-wmf.22 (rMWf77db54ba502)), and it does not seem to work there either. As far as I can tell, the re-enable is just totally and completely broken right now.

(This is kinda amusing because we were looking at the logged-out previews to see how WP did it for regular readers so we could clone it for gwern.net's more advanced popups, and we were horrified to see that re-enabling was implemented as a little near-invisible text link at the bottom of the page, which looks like all the rest of the spam at the bottom of the page. Maybe that explains why, as far as I can tell, no one has reported the bug yet? We went with a little x-ed out speech bubble at the top of the screen next to the dark mode controls, which is far more reasonable. You guys might want to consider doing something like that.)