I want to get more intentional about my fitness and measuring my performance and whatnot. As such, I'm in the market for fitness tracking technology for the first time.

However, I'm very much a Free Software / self-hosted sort of person, and I'm very un-thrilled about how proprietary all this stuff seems. It looks like the sensors themselves are kind of standardized ("ant+", whatever that is), and some of the data formats can be imported and exported, but the bike computers themselves and the companion apps and the online services appear to be trying to become walled gardens.

Short of building a bike computer from components myself, what hardware and software should I be looking into?

Edit: my most immediate concern is figuring out what bike computer to get, to be able to log data from the ANT+ speed, cadence, and heart rate sensors I've already bought (along with a GPS track). I'm considering anything from a Wahoo ELEMNT Bolt V3 ($300), to an off-brand(?) one like a Magene C506 ($100) or iGPSSport BSC100S ($38), to using my smartphone with an ANT+ dongle and the "A Training Tracker" app (Github, Play Store).