I have not found anything on using createBrowserRouter and loaders but this seems to work fine:
https://codesandbox.io/s/react-router-dom-gsap-screen-transitions-p9cp49?file=/src/index.js
( i was having a hard time with codepen, hope this is ok)
Also i'd love to have some kind of "Best Practice" for animating Screen Transitions with React/gsap in the learning section (Sorry for this post if i missed it).