If you exceed your storage quota, you will be blocked from: 

• Creating Google Docs, Sheets, and Slides
• Uploading files or images to Google Drive
• Backing up photos and videos to Google Photos
• Creating new files in collaborative content creation apps like Google Docs, Sheets, Slides, Drawings, Forms, and Jamboard. Others cannot edit or copy files, or submit forms owned by you until your storage usage is lowered. 
• Recording new meetings in Google Meet.

However, you are still able to:

• Sign in to and access your Google account
• View and download files
• Send and receive emails