I don't know why people use fonts served from Google on their websites. Just serve the fonts from the server the site is on. It's like having javascript libraries served by 3rd parties; it's less robust.
Plus in theory fonts optimised for the respective combination of browser and OS. The former probably isn't as critical any more, as almost everything should support WOFF2 (or at the very least WOFF) these days, as for the latter – I know OSs each have their own font rendering peculiarities, but no idea how much the difference might be in practice.
Nowadays, cache is partitioned by website (https://developers.google.com/web/updates/2020/10/http-cache...)