Earlier quoted context omitted.
It is tough. One of the nice things about the Garmin universe is that they have a foundation of open standards that help with interoperability and forward continuity if parts of that universe close. The FIT file format is open. The ANT+ protocol is open I believe, but devices can also use BLE which is open. If I preserve all of my FIT files, and Strava decided to close down, I could upload them all to Training Peaks…
The ANT+ protocol and FIT file format are sort of open. They are well documented and available to everyone. Multiple independent companies do contribute. But ultimately they are controlled by Garmin; they aren't true open standards like WiFi, TCP/IP, or HTML. https://www.thisisant.com/
There is an SDK with a license agreement that is probably more descriptive, but the license terms are not what one expects from measurement instrumentation.