Automatic daily or weekly backups are only possible on desktop for now! If you want to make weekly backups but don't or can't use the desktop app, just add it as part of your weekly review and perform the backup manually once a week. It's very easy and you might be glad you did it someday! OK, pretty please at least backup your data once ☺️.
As of Marvin 1.54.1, your desktop app will make automatic weekly backups. If you have disabled this in the past, you will have to re-enable it. In either case, these backups can be enabled, disabled, and configured by going to ☰→Settings and clicking the Backups tab on the left:
When does Marvin make backups?
When automatic backups are enabled and the desktop app is running, Marvin will periodically check whether a day/week has elapsed, and will save a backup if either the desktop app is in the background (i.e. you are interacting with another program), or if you haven't taken any actions (mouse click or key press) in the last 30 seconds. This is done so that Marvin doesn't interrupt your work within Marvin with a backup.
Marvin doesn't automatically clean up old backups yet, so be sure to clean out old data you no longer need from time to time.
Super secure backups
You could add Documents/AmazingMarvinBackups to your Dropbox, Google Drive, or other cloud storage provider if you want even more reliability!
How to restore backups
See this guide on how to restore backups.