For my second attempt at scanning, I increased the camera resolution from 1920x2560 pixels to 2448x3264. The resulting capture was not as good. Increasing the resolution increased the amount of visible noise on the pictures and they looked a bit overexposed too. I fixed the focal length, but left the exposure settings on auto. I'm using Open Camera on an LG G7 ThinQ.
I still have no sync between my camera and projector, so I had to manually remove blurred frames and duplicates.
This time I sorted out the keystoning by running the photos through ImageMagick and using the perspective transform to re-map the corners of the projection to the corners of a 1440x1080 rectangle. In this case the command was as below.
mogrify -distort Perspective '540,424 0,0 3140,388, 1440,0 680,2290 0,1080 2930,2370 1440,1080' *.jpg
I compiled the frames into a movie using FFMPEG, like this -
ffmpeg -framerate 18 -pattern_type glob -i '*.jpg' -c:v libx264 -pix_fmt yuv420p -vf crop=1440:1080:0:0 out2.mp4
My final result was less distorted, but otherwise inferior to my initial attempt