Support

This is a plugin (Quick Icon - Akeeba Backup Notification). You can read its documentation here: https://www.akeeba.com/documentation/akeeba-backup-joomla/quickicon-plugin.html. You can configure the plugin to change the time period after which it notifies you that the backup is out-of-date, disable the out-of-date notification altogether, and set the backup profile it triggers when clicked. If you would rather not see this button at all you can of course unpublish the plugin.

Kindly note that this feature was first introduced in 2010, back in the Joomla! 1.5 times. After I contributed the Quick Icons feature to Joomla! 1.7.0 back in 2012 it became a plugin. It's been there for 14 years and it's been shipped with both the Professional and Core releases, and enabled by default with a default backup expiration time of 24 hours. Surely you have seen it before. It's been there for 14 years.

I assume that most of your sites were upgraded from Joomla! 3 to Joomla! 4 very recently, around this past summer. Joomla! 3 was stupidly shoving those quick icons into the left hand sidebar of the Joomla! control panel page, which is why you may have missed the fact it's always been there. Joomla! 4 moved these icons front and centre in the control panel page, as was the case with Joomla! 1.7 and 2.5 (and how this feature was designed to work to begin with).