[Bug]: Unable to match a url that ends in an equal sign about react-router HOT 1 CLOSED

Partial dynamic param/splat segments are not supported - at one point partial dynamic segments worked inadvertently but that was fixed in 6.5.0. The param has to be the full URL segment.

You should use a dynamic param or splat route and you can look for access_token=... in the param manually:

let routes = [{ path: '/:param', element: <Param> }];

function Param() {
  let params = useParams();
  if (params.param.startsWith('access_token=')) {
    return <SSOAccessToken />; // or redirect
  }

  // ...
}

from react-router.