They are talking about the firmware that runs on the device. The user front-end to easily configure it is another story. Hopefully it's going to quickly get support for Linux as they are starting from well established Open-source projects for keyboard firmware (QMK and ZMK). If it works like for keyboards, you will be able to configure your mouse with something like VIA that runs on Chrome/Chromium (and maybe one day Firefox ?) using the WebUSB API.

I have 2 keychon keyboards, an old one and a newer one with QMK firmware. Both have worked perfectly well for Linux. The QMK one is easy to configure with VIA once the device permissions are sorted out.