We got rid of it in July 2020. Actually we took out both the 'past' and 'web' links, but people complained a bunch about 'past' so we put it back.
It is not hard to "do it yourself" Start by putting this bit of javascript below into the URL field of a bookmark, give the bookmark a name you like, and put the bookmark somewhere you can find it again:
javascript:(function(){window.location="https://archive.is/"+window.location;})();
Then, when you hit a paywalled site, push this bookmark you made while the paywall site is up. You'll get back either the "view an archived copy" page from archive.is, or you'll be offered the option of actually archiving the page (after which you can view the archived version).
> Removed in July 2020. I removed 'past' as well but there was more pushback about that so I put it back.
Seems it was removed a long time ago (I didn't really notice), but I cannot find any closer reasons why it was removed. My guess is that it wasn't really used much.
https://www.icloud.com/shortcuts/8389264a41c844eb817981fba4f...
Install it, invoke it from the Share sheet, and it takes you straight to the archive results. (When the shortcut asks for permission to access the web page, tap "Always Allow".)