USB N64 Controller and Retroarch is practically incompatible to configure correctly. The only solution I found was to map the n64 controller incorrectly to trick it. Breaks it on all other consoles.
Wireless Game Controller for Windows PC/Raspberry Pi/PS3 Gamepad Rechargeable Gaming Joystick Portable Remote Joypad for Laptop/Desktop Computer,Emulator,RetroArch, Steam,Roblox,RetroPie,RecalBox : Amazon.ca: Video Games
RetroArch] Every Controller is Not Created Equal : r/emulation
RetroArch Controller Setup - Connect and Configure RetroArch Controllers
RetroArch - Playstation Games With PS3 Controller on iPhone iPod Touch iPad (Ep. 5) PS3 Controller - YouTube
Input and Controls - Libretro Docs
Amazon.com: Wireless Game Controller for Windows PC/Raspberry Pi/PS3 Gamepad Rechargeable Gaming Joystick Portable Remote Joypad for Laptop/Desktop Computer,Emulator,RetroArch, Steam,Roblox,RetroPie,RecalBox : Video Games