Could not find any specific information about an "ROCK Pi 4 Plus" so it might be just an abstraction of one of the other Rockpi4 boards. Just give it a shot and test those images, maybe they work, maybe not.
It is worth considering to upload smaller files simply via our forums here. Users might be distracted when being asked to download something from a more or less fishy 3rd party hosting provider.
Userspace upgrades (Focal -> Jammy, Bullseye -> Bookworm) are neither tested nor supported. There is no difference in Debian or Ubuntu flavor in that matter.
Manuals about how to do that may work though if you freeze firmware packages. Otherwise distro-specific kernel will be installed and this will almost certain break boot process.
Confirmed working with a freshly built image. However at least one partition must exist on the NVMe. A completely blank NVMe won't work.
However I think armbian-install received some fixes that might not be included in official 23.02 images. So building own is mandatory (or copy the latest armbian-install script into at least).
Hm did you run apt update beforehand?
Download works for me
apt-get download linux-headers-current-sunxi
Get:1 http://fi.mirror.armbian.de/apt buster/main armhf linux-headers-current-sunxi armhf 23.02.2 [12.0 MB]
Fetched 12.0 MB in 4s (3,045 kB/s)
You do not specifically have to use numpad to enter 1234. The other numbers will work too.
Alternatively you can boot it up with debug serial connected with will do auto-login on first boot.