I’ve come to love and rely on the MMM-Teslamate module and wanted something similar for our new GM EV. While GM doesn’t have an official public API, it’s possible to extract long-lived user tokens and use the same API as the app. Since GM utilizes a bunch of firewall rules on top of their crappy API, it’s nowhere near as useful or timely as Tesla API calls. The API often returns 429s but YMMV. To get a user token, it’s easiest to use https://github.com/metheos/onstar_firefox.
https://github.com/maxbethge/MMM-GeneralMotorsEV