Frameworks like Vue 3 don't actually work on older browsers since it requires ES2016 support in the browsers.. that means IE 11 and older browsers are out. With Svelte you need Microsoft Edge (IE 11 is not supported). Also, it requires Firefox 74 (released in 2020) or newer Firefox versions.
With React, you can make it work with older browsers using Polyfill etc.
As it is, there multiple browsers supporting different levels of features.
That's the whole reason why frameworks are made in the first place dating back to jQuery.