I know the community is working on a project called OpenCentauri, an open firmware for the Elegoo Centauri Carbon (great printer and amazing value for the money, but it uses a closed variant of Klipper, who knows what it's doing in the background)
You also have the DIY Voron kits, and Sovol produces Prusa-likes and Voron-likes that usually use open firmware.
Just avoid Bambu as somebody who owns an A1 (set to LAN only mode, using a microSD card to transfer print files), as aside from the lock down shenanigans and attempting to take down forks of their Bambu Slicer software (which itself is a fork of a fork), they also use a closed firmware and are heavily promoting their cloud services. I also heard that Creality is one to be cautious of too.
I am moving to Piefed at scallisto@retrofed.com (https://retrofed.com/u/scallisto)