The "true" game content is only about 335 MB . The remaining space is filled with random "garbage" data used to pad the physical disc, which is why raw ISOs compress poorly compared to "scrubbed" versions.
There are several apps available on the Google Play Store that emulate the GameCube. You will need a decently powerful smartphone to run TTYD smoothly. Paper Mario The Thousand Year Door Gamecube ISO...
But physical copies are rare. A complete-in-box copy can sell for over $150 on the second-hand market. Nintendo did release a Switch remake in 2024, but purists and speedrunners still crave the original GameCube experience. This is where the enters the conversation. The "true" game content is only about 335 MB