Welcome to the community.
On the Framework-13, the keyboard is not usb. Like most laptops, it’s just a key matrix directly connected to the motherboard. Connector pinout. The Embedded Controller handles it.
On the upcoming Framework-16, the keyboard will indeed be usb connected and running open source qmk firmware on a rp2040 microcontroller within the keyboard module. Whether the input modules share a USB controller with other usb devices or ports I think is unknown at this point.
Framework has been posting Deep Dives about aspects of the Framework-16. There is one planned for the keyboard. The second Deep Dive was posted 2 weeks after the first. If they keep up that rate, you could calculate when the keyboard one will be posted, presuming they will be done in the order listed.