AFAICT, there is no quickbar navigation (keyboard shortcut) available to get to the backups page (or the other two hassio supervisor page tabs system and add-ons).
Related to this, the “search” function on the configuration page will not find anything for backups because there is no quickbar shortcut.
I understand that this due to the historical separation for the supervisor, but given that the configuration pages were unified a number of releases back, this seems like a WTH.
As @tom_l points out below, you can navigate to “Hassio” to get to the Add-ons, Backups, and Supervisor page.