Fingerprint sensor on arrowOS definitely worked for me.
I think k4y0s can tell you more later.I wasn’t there all the time, I also played with another project or just talked with people 
But there is a command to get rid of the shutdown in 30 seconds, it’s “dm-verity enforcing” or something in adb, even works from twrp.
I think twrp caused some issues because it modified some partitions by mounting them read write.
Playing with vbmeta made my phone just showing a black screen for hours because we crashed aboot, or just showed the fairphone logo and froze. Pressing volume down while turning it on always gets you into fastboot mode.
I brought my UART adapter home this time.
GSI AOSP 9 without gapps (vanilla-nosu) does boot. The GSI option to show the navbar seems to be buggy (on fp3). GSI should also allow to tell on which side the volume and on/off buttons are placed -.-
Maybe we should hack some patches together for that.
EDIT: I typed too long 