SOQuartz Software Releases
Manjaro ARM
Manjaro ARM is a user friendly rolling release distribution, based on Arch Linux ARM.
pgwipeout's Quartz CI
pgwipeout's Quartz CI includes a Debian installer image for the SOQuartz, with the CM4 I/O board as the base board. To download, click the "Download artifacts" button on the right hand side, unzip the archive and take a peek inside the "images" folder to see the selection of pre-built images. Assuming your target device is /dev/sdX, you can flash it with:
sudo -i xzcat /path/to/rk3566-soquartz-cm4.dtb.img.xz > /dev/sdX
You will need 3.3V UART at 1.5 mbauds (1500000) to access the interface.