Still good to know that at least it's supported, even though it needs a custom (non-mainline) Kernel for now .
I'm a bit surprised they are still using 6.1 Branch, but fair enough, that is Longterm Support (as would be 6.6 and 6.12), but kinda weird they are using such an old Version.
The exact Version they seem to be using is 6.1.115, released 2024-11-01 (01-Nov-2024), as opposed to latest 6.1.140 released on 2025-05-22 (22-May-2025).
However the Build Log that Igor pointed me to was 6.1.99-vendor-rk35xx, so yet another Version. But maybe that isn't the latest Build or ?
Installed Packages in that Log point to 6.1.115
ii linux-dtb-vendor-rk35xx 25.8.0-trunk.53 arm64 Armbian Linux vendor DTBs in /boot/dtb-6.1.115-vendor-rk35xx
ii linux-headers-vendor-rk35xx 25.8.0-trunk.53 arm64 Armbian Linux vendor headers 6.1.115-vendor-rk35xx
ii linux-image-vendor-rk35xx 25.8.0-trunk.53 arm64 Armbian Linux vendor kernel image 6.1.115-vendor-rk35xx