Hello, upstream maintainer here. Please see this merged upstream PR
<https://github.com/bit-team/backintime/pull/1899>
The user-callback scripts not part of upstream repo, installed in
"/usr/share/doc/backintime-common/user-callback-examples" (via make) and
added to the user manual.
The integration into the GUI is still missing (https://github.com/bit-team/backintime/issues/1331).
Regards, Christian Buhtz
