I wrote up a mostly step by step tutorial for the Ubuntu Focal (20.04) install process with 5.7 kernel and such.
http://forum.pine64.org/showthread.php?tid=10279
It's a pure 64-bit install, but you can easily create a 32-bit chroot to test 32-bit software in there as well. I've got a 32-bit Ubuntu install for media browsers (Spotify and crew - the DRM modules for ARM are 32-bit only).
For testing, though, there's really no reason to put the install on the eMMC. Just use the install on the SD card - update the kernel if you want, but you should be ~fine once you boot from the SD card with the image on it (I think it's a 5.6 kernel without all the hardware acceleration, but that's fine for testing builds).
http://forum.pine64.org/showthread.php?tid=10279
It's a pure 64-bit install, but you can easily create a 32-bit chroot to test 32-bit software in there as well. I've got a 32-bit Ubuntu install for media browsers (Spotify and crew - the DRM modules for ARM are 32-bit only).
For testing, though, there's really no reason to put the install on the eMMC. Just use the install on the SD card - update the kernel if you want, but you should be ~fine once you boot from the SD card with the image on it (I think it's a 5.6 kernel without all the hardware acceleration, but that's fine for testing builds).