For everyone interested in full control of OLED and battery status on vanilla OpenWrt 23.05, I've created small script intended to run in background and update display every minute. Script have dependencies, but they all are packaged, so you won't need to fiddle with OpenWrt build system to have all features.
Details here: GitHub - pekmop1024/gl-e750-mcu-oled: GL.inet GL-E750 MCU OLED script for vanilla OpenWrt