Konakona
https://dolphin-emu.org/ is the only gamecube emulator.
They aim for emulation accuracy and compatibility, meaning speed is not a concern (as you cant have both speed and accuracy). The more accurate you make the emulator to the original hardware, the higher the requirements are to run it.
And dolphin has VERY high requirements. (need a modern intel cpu, preferably the newest haswell generation cpus)