Hey,
I wanted to get N64 working on Libreelec so I vibe-coded this addmon, it runs RetroArch (Lakka v6.1 build) plus the Mupen64Plus-Next N64 core, configured for smooth gameplay on a Raspberry Pi 4 (2 GB or 4 GB) running LibreELEC.
I tested it with Mario 64 and it worked smoothly. So if this works for anyone else, or needs tweaking, would love to hear 
GitHub - guysoft/script.retroarch.libreelec: Kodi addon: RetroArch + mupen64plus_next for LibreELEC on Pi 4/5
Kodi addon: RetroArch + mupen64plus_next for LibreELEC on Pi 4/5 - guysoft/script.retroarch.libreelec
github.com