I have the same frustration. It appears the Mali T864 support by Rockchip is very poor.
I might try the Panfrost driver. Right now I'm using the xorg fbdev driver and the llvm meda driver. It's a little faster than
the terrible Mali Blobs but it's still not fast enough for good opencv performance, bzflag is 12 frames per second, armangand is 12 frames /sec. Not a gaming mini PC that's for sure. I modified and recompiled Plex Media Player to use DRI/FBDEV for video out. I can get 1080p with no dropped frames. I can't play video on my 2k monitor.. it's a slide show.
My confidence in Rockchip right now is very low. They don't answer emails. They don't seem to be making headway.
Friendly Elec's hands appear to be tied because Rockchip Support sucks. It's too bad. On paper the NanoT4-PC4 has great specs, but the poor Linux support
I may end up staying with the NUC for my designs since ARM does not have a solid open MALI driver and library.
I can tell yo my NUC Hades Canyon is EXTREMELY fast with BIONIC Beaver and my TiNKERBOARD can play 3D games better than my NANOPC-T4. It's too bad, I really like the performance of the NVME on the NANOPC-T4 and the high speed USBC. Rockchip dropped the ball when it comes to GPU support. It's terrible! Also on Android NO NVME support.