RK3399 works quite good with mainline kernel, easily to check out with Armbian if You want it.
Official kernel release was 5.1 and it was promise that Rockchip will upgrade it to 6.1, @jack shared that it should happen before end of Q2: Why is Radxa giving up on software support? (end of this month)
So we may expect new releases for all RK3399 boards from radxa,
If You are using only software, then just go with mainline, there are some problems with details and hardware interfaces, but mostly is just ok.
Probably those wait for new official kernel and documentation, for now not worth to spend time on this at old 5.1 kernel. Maybe someone from @radxa can share more details on this. Promised kernel was originally scheduled to Q3 2024.
It’s still great board of pi4 era, but we already few steps forward 