What do you see on the top left corner of sidequest when your headset is plugged ? Could you show me ? You should try another USB cable and be sure its an OTG cable.
I asked yyou for the developer mode because ome people imagine this is the developers options in the headset and didn't check their smartphone app.
Anyway you have plenty other solutions to enable ADB here : https://anagan79.itch.io/quest-games-optimizer/devlog/360229/enabled-adb-wifi-vi...