Typst is “A new markup-based typesetting system that is powerful and easy to learn”. It’s written in Rust, and particularly attractive because, while providing a CLI interface, it is a proper library that you can easily incorporate into your progress to produce documents. Protip: If you do so, have a look at sys.inputs, it’s awesome!
I think what Kualk@lemm.ee is getting at is that Typst also a paid web app developed by a for-profit company. This same company is who manages the github repo for the Typst language compiler. They seem to take issue that this post is promoting a partially open-source project for a for-profit company.
But typst itself is fully open-source. Saying it’s a „partially open-source project” is a mischaracterization. You don’t need to use the web IDE and it’s not strictly part of the „typst project”