How to enable USB debugging in LineageOS 14 on Moto G2014? I want to build LineageOS 15 from source following the titan image build guide which requires the transfer of vendor specific files and thus an adb connection after enabling USB debugging.

I didn't find a LineageOS-specific guide on turning development tools including USB debugging on, so I went with my Android knowledge of tapping 6 times on the build number in the phone settings. This shows a screen with my home screen background and the LineageOS emblem. The emblem responds to taps anywhere on the screen by changing it's styling, but nothing else. I can go back and use the phone including repeating the journey to the emblem screen.

I get that these settings should be hidden for non-dev users and don't need to be reachable very intuitively, but that's covered by hiding the function behind the 6 taps on the version item. After that the proceedure to enable development features can be intuitive again.
I went with my Android knowledge of tapping 6 times on the build number in the phone settings. This shows a screen with my home screen background and the LineageOS emblem.


Despite what you claimed, you've tapped the wrong place. Tapping "Android version" will show a big N; tapping "LineageOS version" will show you the LOS logo; tapping the actual "Build number" item, which is the second-to-last item in the About phone menu, is what you should go for.

On top of that, it should be tapped 7 times, and each tap should notify you about needing more taps to unlock Dev Options.