is there any android 8.x or newer available for the roc 3328-cc, or sources to bake one by myself?
You may have to bake it yourself as Android 9 is being worked on. The 8.1 repo is here: https://drive.google.com/open?id=1sp9OIy95JCIKNbIwUkV0ogTddRMRMIcA
I'm busy making an Android 8 firmware for ROC CC.
There is just some small things I still want to fix to improve the user experience.
We really need Android 9 since it uses a newer kernel and has improved video playback, Magisk systemless root & TWRP Recovery support. Rockchip also works on Android 9 mainly now, so Android 8 support will be limited.