I would probably just use Slack and Slack-bots for a low-code approach to this. Are there major downsides? I don't believe you would need to pay for Slack to use primarily for up to a few dozen Slackbot messages per day.
./backup-server.sh; curl -d "backup done" ntfy.sh/shake_backups
[1] https://news.ycombinator.com/item?id=29719738