Posted a solution here. Duplicating below.
For anyone else re-using Lucas’s code above (thanks a ton @lstyles, your repo is literally the only example I found online for vue3), if you’re having trouble with redirects working correctly you need to add this line:
state.error = null;
after this line:
const {appState} = await client.handleRedirectCallback()
in Lucas’s index.js file.
I spent more time than I’ll ever acknowledge learning this:)