Novice question: Pinebook Pro does boot (does it?) but black screen

[KC9UDX]

You might want to try Debian, which was the default operating system for the Pinebook Pro before Manjaro. It has proven itself much less likely to get you into these kind of situations.

Now that you've booted though, this is the time to make copies of anything you'd like to save that's on the eMMC. Then you can decide if you want to fix or replace the Manjaro installation.