Try a hard refresh or open the app in incognito mode (or a different browser) — cache or session/cookie issues can sometimes prevent the external-user landing page from loading properly.
So personal gmail works with pw, gmail workspace = broken weather pw or google connect on one account but works on a different workspace. If you can, I would compare the 2 workspace security configurations. It seems like something is blocking one of them.
Is the Workspace-managed Google account subject to any additional security restrictions (e.g. SAML SSO, enforced MFA, domain-wide policies) that might interfere with OAuth sign-in?
Did you configure Google OAuth / “Sign in with Google” SSO for that workspace domain (i.e. with proper OAuth client + authorized redirect URIs)?
Have you looked in the browser console yet to see if there are any errors or clues? That might be your next step.
Otherwise, if you have time, office hours is probably your best bet. If they can’t solve it live with you, they will reach out to the appropriate department to investigate further.
That is very odd, it seems like you have the permissions on the app set up correctly.
The fact that the page loads and has some JS/HTML on the screen (although empty) leads me to wonder what the browser console is saying, as @Shawn_Optipath mentioned
Since if it was permissions they would likely be given an error message or redirected.