Lightroom Classic will only sync Smart Previews to the cloud not your originals. Therefore, it is of no help with backing up your files from within the application.
The 1TB storage is only really of use when using Lightroom CC, Lightroom web and/or a mobile device. In your case, and to avoid complicating matters (Lightroom Classic and CC on the same computer is a recipe for a migraine) by also installing Lightroom CC, you can upload your raw files directly to Lightroom web. However, before doing so, I suggest you disable sync in Lightroom Classic otherwise you'll end up with a Virtual Copy in Lr Classic for every image you uploaded to Lr web. See this document for details on how to access Lightroom web Learn to use Adobe Photoshop Lightroom CC on the web To upload image to Lightroom web, you'll need to open it via your web browser then select the '+' button as shown on below screenshot. When the upload is complete you'll be asked to refresh Lightroom web. When refreshed you uploaded images should now be visible in Lightroom web.
