Personally I have a flask app deployed on heroku that posts a message to a Discord webhook just by visiting an url. So in my case when I use ssh to run long tasks I have at the end "curl https:// <server> .herokuapp.com/?Finished" and as soon as that commands is executed I receive a message either at my phone or computer (through a channel in a personal discord server).

Probably is a bit of a 'hacky' way, and using different proprietary services (heroku and discord) but it works, does it fine, and it's free! (And it was also funny and quick to develop by myself).

The source code is on Github too! https://github.com/TrianguloY/ping