There is an easy way to back up your data: Google can send you a download link by email , with which you can download the file. By the way, this is possible not only with data from Gmail, but also from all other Google services, such as Google Calendar, Google Photos or browser history. You don't want to backup the files on your device, but rather in the cloud? No problem: Google offers the option to save the file to Google Drive, Dropbox, or Microsoft OneDrive.
If you change your mind later, you may be able to get your account back with your regular email address . However, do not trust that the data is still available, especially if you deleted the Gmail account a long time ago. In this case, you usually won't be able to retrieve your emails. Therefore, it is advisable to make a backup before deleting it.
If you use your Gmail account as part of a group (such as school, college, or work), you may not be able to easily delete it. In case of problems, contact your email group administrator.