Alright, didn't know they are still there. Well as mentioned media won't receive any further updates since all functionally is merged into standard branches.
Anyway, Rock64 is rk3399 I think and you should be good to go with mainline kernel, either current which is 6.12.y or edge which is 6.14-rc7 atm.
The branches at https://github.com/armbian/linux-rockchip are made from Rockchip BSP code and mostly for rk35xx socs. I don't think there is much work there for rk3399.