Someone might notice a pattern, e.g. type of texture going bad here and know what it could be. Can you try running Swiss on it to see how that looks to give us a rough guide of what's going wrong? If you boot Swiss and all fonts look garbled then maybe there a problem with the MX chip or connection...

About 15 years ago I got this Gamecube, used it for maybe a couple years and then it started having problems. the text would look all weird at the startup screen, some games would also have text looking garbled, and others would always freeze at specific parts, some wouldn't even make it past the ti...