Developer options are hidden on every Android device until you ask for them a specific number of times. Here is the whole sequence on a Seeker — tap through it on the phone below, and the checklist keeps score.
The computer's RSA key fingerprint is:
Nothing happens for the first three taps. On the fourth, Android starts a countdown toast — “You are now 3 steps away from being a developer.” Keep going to zero and the hidden menu is unlocked for good.
A new Developer options entry now sits in the System menu. Inside it, flip USB debugging on — that is the switch that lets adb see the device at all.
Pull the shade down from the top of the screen and tap the USB notification. Change PTP (Transferring photos) to File transfer / Android Auto.
The phone shows your laptop's RSA key fingerprint and asks whether to trust it. Tick Always allow from this computer so you are not re-authorising after every reconnect, then tap Allow.
$ adb devices List of devices attached — nothing yet —