For security and compatibility reasons, iodéOS uses user build type instead of user-debug (with the ability to enable additional debugging).
As a consequence root access and debug capabilities are not available in developer mode.
If you still want to have root access, you would need to flash a more permissive recovery than the default one such as TWRP 19 and flash Magisk 16 from the recovery using the following commands:
adb sideload Magisk.apk
And after reboot:
adb install Magisk.apk