Install a Raspberry Pi Pico in your GameCube console.  This is the most advanced "modchip" for a GameCube. A lot more information can be found here on what it does.

A comprehensive install includes the following:

• Install latest firmware of PicoBoot to the Pi Pico
  
• Install the Pi Pico inside your GameCube
• Install a new battery holder + battery in the GameCube (they all lost power now and can't save settings or clock)
• verify operations

NOTE(S):

• A working compatible GameCube must be provided. It is recommended that a DOL-001 GameCube with the SP2 port on to bottom (open it to confirm it's there) Without this port, you won't be able to use an SD2SP2 adapter. Th SD2SP2 is required to load Swiss which will allow you to play out of region games, ISO images of game backups, etc.
• The Pi Pico + SD2SP2 can be provided for an additional fee.