I’ve found some new images for RockPi4 with the latest kernel like DietPi, Manjaro, Armbian. What is the proper way to try it on my RockPi4? If I write the image to an SD card or an NVME disk, RockPi does not boot. eMMC is connected and contains the working Ubuntu 18.04 OS.
Thank you for pointing me in the right direction. The problem in my case is related to the SPI flash with UBoot. When I disabled it by connecting pins 23 & 25, I can load the latest DietPi and Armbian from an SD card.