Maybe [SOLVED] Network Connections Priority - LibreELEC - LibreELEC Forum
cp /etc/connman/main.conf /storage/.config/connman_main.conf
nano /storage/.config/connman_main.conf
^ edit the order of PreferredTechnologies so wifi is before ethernet and then save and reboot to effect the change. When wireless is connected it will become the internet routed connection.
PreferredTechnologies = wifi,ethernet,cellular