Wrong console?
N64 emulators are all pretty bad (inaccurate, use a decent amount of resources) and upscaling is relatively expensive. At least, way too expensive for an rpi to handle.
It will work fine as an emu at 240p though
Usually after you get source releases to games, you get people that port them to different platforms. Like how we had Doom on iPods and Kodak digital cameras.
I haven't tested N64 games on a RPi personally, but I imagine it would have no trouble with it, and there seem to be several retro-gaming projects that involve N64 games and use the Rpi.
Pi format is still fun to tinker with and I encourage you to get one if you're at all interested. The 3b+ just wasn't the right tool for the job in my case. I haven't tried the pi 4, however.