Had the same problem but the kernel8 thing just broke all my games (black screen whenever I tried to load any game).
The solution that worked for me was to add these lines to my retroarch config file:
parallel-n64-cpucore = "cached_interpreter"
mupen64plus-next-cpucore = "cached_interpreter"
as per this thread: https://www.reddit.com/r/raspberry_pi/comments/18pus3g/raspberry_pi5_retropie_n64_how/
For context, I just got my Pi 5 8GB and running full Raspberry PI OS. Installed retropie and all the emulators from source.