If you click on the three-dot menu, there's a small caret button you have to click to show more of the pill buttons at the top, and one of them is "Cached".
It feels like every time I need to use that button it's moved somewhere new.
However, this option is hidden for me on every result I’ve checked. Pages posted several years ago, pages posted within the past couple months, Reddit pages, StackOverflow pages, etc. Even pages from Google itself are missing a cached page option for me.