i commented it already in some beta threads of 5.27 here and i came to same conclusion.
I tried to use all emu cores for N64 on latest batocera, recalbox and retropie versions for the RPi4. The results are in every case the same. Slowdowns, many glitches, problems with shadows, etc.
All in all the whole emulation quality for N64 is better on RPi3 as on RPi4 at the moment. If i made such comments in the past, I got the feedback, that the emulator or the core is the problem. I guess it is a bit more difficult especially because of the new graphic chip in RPi4. Unfortunately, I found until now, also not the main issue of the bad N64 emulation, but I guess it should be well-known at the developers and it's not only a topic at Batocera.
It would be nice, if a developer could maybe comment that too, what are the real issues there and if there are possibilities for a smoother and better emulation of N64. Maybe some parts of the cores has to be re-written. Or maybe new graphic driver could help too. As I know the vulkan driver is already in a late state of development.
Never the less, I hope at least, that this will be discussed more in future, that also the users have an idea, in which direction it will go, or what could be possible.