You can install the Google Forms add-on from the Google Marketplace with your Gmail or Google Workspace account.
If you press the "Install" button, it shows a loading circle on a white window, but doesn't move on to 'accepted' window.
You can resolve this issue by signing out of multiple Google accounts.
If you are unable to add the add-on to your Google Forms because the install button is disabled and grayed out, you need to contact your Google Workspace admin to whitelist the app.
Please see this
page detailing how your admin can add the Google Forms add-on to your domain's allowlist.