Update as of July 2024:
How to get this mod working:
On Dolphin go to "Settings"
Go to "Paths"
Add a Game Folder containing your BFBB rom.
You should see BFBB on Dolphin's home screen.
Right click on BFBB and go to "Properties"
Press the right arrow all the way until you reach Filesystem.
Right click on the Disc and click "Extract Entire Disc"
Locate the folder you extracted the disc to.
Go to the "sys" folder.
Rename the bfbbmulti3.dol to main.dol.
Drag and drop the renamed bfbbmulti3.dol file into the folder.
Replace the main.dol with the new one.
Should work now!