A couple of people have been succesfully using a IDE-msata housing for Morphos on the Mac Mini G4.
I also have a working setup.

However, I also have some IDE-CF (Compact Flash) adapters laying around that I have as spare for my Amiga’s.
A IDE-CF with CF card is probably a cheaper way than getting a IDE-msata housing while as an Amiga enthusiast, you probably already have the IDE-CF adapter or at least an CF Card laying around.

The trick here is. Make sure you connect the IDE-CF Adapter with the CF Card facing down.

There should also be jumpers on the adapter,  so you can put them in Master (connect pin 1 and 2) or Slave (connect pin 2 and 3).
To get the adpater to work in a Mac Mini G4 however, you have to remove the jumper entirely. Which will put it in Cable Select (I’m assuming). Put the jumper in a save place. These things were everywhere 5-15 years ago, but not anymor.

Now continue the instructions on the MorphOS website.

Download theISO image from MorphOS – Downloads (morphos-team.net)

Follow the guide at: MorphOS – USB Boot & Installation – Guide (morphos-team.net)

On the MorphOSBoot media, in Tools, you can find HDConfig, which you can use before the installation, to wipe the CF Card. Although it’s probably better to wipe the CF on a pc before you start the proces.