Looks like this is something backrest could integrate support for with https://github.com/gen2brain/beeep .

Hook types are relatively straightforward to add to the hook registry https://github.com/garethgeorge/backrest/tree/main/internal/hook/types though some amount of plumbing is needed for UI support.

I agree that native support is a good idea, this is fairly low priority for me as scripts are a solid workaround -- but it is the most common scripting use case from what I see in discussions. Current projects on my plate are multihost synchronization and improving the form system, but I've tagged it as a good first issue as it's pretty approachable.

scripts are a solid workaround

Yes, scripting gets the basics done (notification per executed backup job).

Looking at how backup notifications are done on Windows 10 or on macOS, I think those solutions are, however, more reliable than scripts. For instance, backups might start only if the computer is on power supply or if it can reach a specific host or network. Now, should those conditions never be met for instance for two weeks or a month, Windows and macOS will create a notification to make users aware about this. Another example is a monthly backup job I scheduled using resticprofile including notifications on errors, but that job didn't execute for months so none of my notification scripts got actually triggered.

On both cases, you'd be receive a warning on Windows and macOS.