Add QMK to your older K Series - eviltoast
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sonixqmk.github.io
The Sonix QMK community has ported many Sonix MCU boards from the like of womier, redragon and keychron to the open source keyboard firmware QMK.

If you have an older K series Keychron keyboard that includes a Sonix MCU you can flash to a custom firmware that supports QMK/VIA so you dont have to use the garbage stock software.