Google has announced that starting on August 22nd you will only be able to create new forms by using the current, AKA "new," version of Google Forms. Also beginning on August 22nd all existing "classic" Forms will be automatically updated to the new or current version of the Google Forms interface.
Any submissions that have been collected through the old version of Google Forms will not be affected by the automatic upgrade to the new version of Google Forms. Any questions that were written in the old version of Google Forms will not be affected by the upgrade to the new version.
My Practical Ed Tech webinar Google Forms and Sheets for Beginners will show you everything you need to know to get started with the latest version of Google Forms.