To play N64 games, you need horsepower. Install the "PS1 Classic Overclock" mod (available via the Project Eris Mod Store). This raises the CPU from 1.2GHz to 1.5GHz. Be aware: This increases heat slightly and may reduce the lifespan of the console (though anecdotal evidence suggests it is safe for short play sessions).
If you want to turn your PS Classic into a definitive retro emulation box while keeping the original look and feel, Project Eris is the best all-in-one solution available today . ps1 classic project eris