Oh, I was expecting the “ROCK 4 SE” U-Boot build to define the “ROCK 4 SE” device tree as default, but obviously it does not. We need to set it in /boot/dietpiEnv.txt then, with the fdtfile= variable.
EDIT: Oh, the kernel/dtb package shipped by Armbian via their APT repo does not contain the ROCK 4 SE device tree yet. Probably it works when just updating the kernel. @janno can you test this:
cd /tmp
wget https://dietpi.com/downloads/binaries/linux-{image,dtb}-current-rockchip64.deb
dpkg -i linux-{image,dtb}-current-rockchip64.deb
rm linux-{image,dtb}-current-rockchip64.deb
reboot
If not, then after above:
G_CONFIG_INJECT 'fdtfile=' 'fdtfile=rockchip/rk3399-rock-4se.dtb' /boot/dietpiEnv.txt
reboot
I also just triggered a new image build with both above things done, but I am still curious whether the bootloader picks the correct device tree automatically, when it exists.