If the Backupery for Slack is installed, a workspace owner and other members are not explicitly notified, however, any user can see the installed application if the following steps are performed:
- Click Apps on the bottom left:
- Browse Apps box will be shown:
The application is shown here along with who and when installed it.
Please also note, that if you add Backupery for Slack application to a channel, all the members of the channel can see that the application was added: