Goodboy Galaxy supports two different kinds of rumble:

• Game Boy Player mode
  • Requires a GameCube with the Game Boy Player peripheral.
• Fallback mode
  • Works with a variety of other carts / devices / emulators, such as:
    • EZ Flash Omega Definitive Edition
    • insideGadgets rumble carts
    • Analogue Pocket with DS Rumble Pack
    • MiSTer
    • mGBA core in RetroArch

Once Rumble is enabled in the Options menu, the game will automatically detect which of these two modes to use.

NOTE: The physical carts from First Press don't have a rumble motor, but they work with the Game Boy Player (and potentially GB Operator in the future).

Many emulators rely on the Game Code (a.k.a. ROM ID) to detect whether a game makes use of the rumble feature.
This includes MiSTer, Analogue Pocket w/ DS Rumble Pack, and mGBA.

To make the rumble feature work on these platforms, a .bps patch is available here: https://goodboygalaxy.com/files/goodboy-1.2-rumble.bps

This patch simply changes the ROM ID to match Drill Dozer (a well known rumble game).

You can apply this patch to your goodboy.gba ROM using Flips or this simple online patcher.