I haven't used it, but there's also Avocado OS [1]. Myself, I use Yocto for our embedded build. It's not perfect but for our application, which involves building a bunch of software that uses both Swift and Flutter for an embedded audio product running on a RPi CM4, it works just fine. Shout out to Mender for A/B updates.

[1] https://www.peridio.com/avocado-os