Yea it can be done, but it requires thoughtful implementations and planning if you are working within a mature system.
We had/have a similar problem where things began with "a sprinkle of js here/there" and then over time those islands became much bigger and encompassed more and more functionality. Entire backend templates were ported to the JS framework and then the page with load and then stuff would pop in after the DOMReady event was fired and the JS booted.
I've been working backwards to remove many of these changes and handle them server side if possible or at least give a better UX while the frontend is getting ready. It's not easy!
In a perfect world, we could run the output of the PHP backend through a JS SSR endpoint and hydrate the few necessary components into full HTML, but unfortunately, many of today's JS SSR tools are only available if you use the meta framework as well.
What's going to be fun over the next year is finally deciding if we should go "all-in" on a JS frontend (using Inertia.js for the communication with the backend) or go back to PHP entirely and try to leverage more browser capabilities. There's not really a right/wrong answer but if marketing want's to keep adding flashy features, having the flexibility of JS would be handy.