Google started informing users on the G Suite free legacy plan that it decided that there would be no no-cost migration for users who still need an email account.

> Note: If you no longer want to use Gmail with your custom domain or the ability to manage multiple users, you’ll be able to join a waitlist in the Google Workspace Admin Console for a no-cost option in the coming weeks.

https://support.google.com/a/answer/60217?product_name=UnuFlow&rd=1&src=supportwidget0#nocost