K4 Wireless Mechanical Keyboard (Version 2)

First reset to factory defaults Unspecific, but par for the course is resetting to factory defaults and reflashing the keyboard firmware. Though reflashing the keyboard firmware is risky business for the original K series with proprietary keyboard firmware (which includes the K4 V2). It is a differe

You can try completely disassembling it, gently polish-cleaning it, and looking for damaged traces or traces bridged by dried debris. Like this: https://imgur.com/a/zebrawood-board-disassembled-cleaning-XDKa8sW This would be the closest replacement: https://www.keychron.com/products/keychron-k4-qmk-

(K4 V2 is in the original K series. Only K4 V3 got QMK support.) It probably doesn't apply to the original K series, but RGB light off is a problem for some later Keychron keyboards.

Re "Keychron Launcher doesn't detect the keyboard even if it's directly connected via USB (with data transfer cable); VIA isn't compatible with the K4": Yes, the original K series, including the K4 V2, has proprietary firmware and doesn't support the Via protocol. (K4 V3 got QMK (and thus Via) suppo