SSO across domains failing because of third-party cookies

We have implemented an iframe to load a third-party app within our application wherein currently we SSO to the app using sessionCookieRedirect (like mentioned here) and once complete, we open the app inside an iframe.

Now that a lot of browsers have started blocking third-party cookies, sessionCookieRedirect doesn’t set the cookies anymore and hence the implementation is now failing in some browsers.
Is there any workaround for this?