How do you check google's cached version of a page now?

For someone else's page there's also the Rich Results Test. It accepts any URL and shows you the rendered HTML Googlebot gets, which is often what people actually wanted the cache for.

You can't any more, Google retired the cache link and the cache: operator in 2024. If you own the site, URL Inspection in Search Console is the replacement. "View crawled page" shows the HTML Google last fetched, and the live test shows how it renders now with a screenshot. For someone else's page, the Wayback Machine is the closest thing.