From a forum post in that thread you linked: [15:00:37.296] OS: Linux, 4.4.213-rockchip64, #5 SMP Fri Apr 16 17:25:31 UTC 2021, aarch64
This means the Armbian image is using the Rockchip 4.4 vendor kernel. LE has no interest in that kernel. I'll let others comment on whether there is any usable mainline kernel support.
The post has two images of Armbian. One based on the Rockchips kernel and another in the mainline kernel. If I'm not mistaken.