Some advice I read for open-source projects that do not have any telemetry in their software, on how they can still get some passive insights into user behavior:

• Instrument your web docs. If you want to know how people are using your CLI tool, make a set of docs around the use cases you’d like to understand best, and see how they perform over time. Look at what people search for within your docs.

• Instrument your downloads. This can be a rough metric to understand usage and what operating systems your users are running.