How to install OpenWRT on Zyxel Multy M1 (WSM20)

How to turn a Zyxel Multy M1 (WSM20) whole home mesh WiFi router system unit into an OpenWRT router. Note: This removes the Zyxel WiFi mesh functionality and turns it into a router or access point only. How to WiFi Mesh backhaul on OpenWRT on a WSM20:    • How to WiFi Mesh on OpenWRT (Multy M1)   For those on stock firmware: How to factory reset a Multy M1 WSM20:    • How to factory reset a Multy M1 WSM20   How to add another Multy M1 WSM20 without the app.:    • How to add another Multy M1 WSM20 without ...   Zyxel Multy M1 (WSM20): A detailed look.    • Zyxel Multy M1 (WSM20): A detailed look. D...