pi zero is probably too slow to run anything other that mario 64 nicely. pi2 doesn’t do much better.

menus are corrupt in rice plugin for mario kart 64. try glesn64 plugin. to change plugins: https://github.com/RetroPie/RetroPie-Setup/wiki/runcommand

select is the default fire (Z trigger) button. to change config: https://github.com/retropie/retropie-setup/wiki/Nintendo-64