@jdonald wrote:
Welcome, and nice work @Hal58!
Comment out the line near the end by adding a '#' in front of 'dtoverlay=vc4-fkms-v3d'.
Well that kind of hamstrings the whole system leaving it without GL or GLES, although expected to be necessary for Ubuntu 18.04 which uses an older version of Mesa. It's described in that thread on the Pi forums.
If they're right and it's only Mesa that needs to be updated, would be great for someone to try out a Mesa 19.1 build on Ubuntu 18.04 + Pi4 to fix the fkms overlay. See this Mesa cross-compiling guide by Eric Anholt. Running that procedure on an Ubuntu 18.04 x86_64 system should be enough to make a whole set of libraries that's libc-compatible with Ubuntu 18.04 armhf.