In brief: Google's cached search results has joined the infamous Google Graveyard of features and services killed by the Mountain View tech giant. In response to a recent X post about the missing feature, Google Search liaison Danny Sullivan confirmed the cache link has been retired. Sullivan said the feature, which was one of Google's oldest, was meant to help people access pages at a time when you couldn't reliably depend on an Internet connection.
Things have improved greatly since then, so Google decided to discontinue the feature.
Cache links showed a snapshot of a webpage as it appeared when it was indexed by a web crawler. The links were indeed helpful when trying to view the contents of a page that wouldn't load for whatever reason (maybe your connection was being spotty, or the source was getting hammered with traffic), but could also be used to chart page edits / revisions and get a glimpse of content that had since been taken offline.
Sullivan said he personally hopes Google will replace cache links with links to the Internet Archive in the About This Result section (accessible when clicking the three dots beside a search result). The liaison said Google would have to work with the Internet Archive on the feasibility of baking in Wayback Machine results, and that it involves people beyond him, but believes it would be a nice addition nevertheless.
I tend to agree with Sullivan's stance that the Wayback Machine would be a great substitute. Should the integration come to fruition, however, it would be nice if the results could somehow be sped up. In my experience, it can take quite a while to dig up an archived page using the service. Google's cache links, by comparison, were much zippier.
For now, it is still possible to use the cache: operator, but Sullivan said that will be going away soon as well. To use it, search cache:https://www.example.com using Google (replacing example with the URL you want to see cached results for).