I have an iMac 2013 running High Sierra with a fusion drive. The fusion drived used to be an internal SSD and hard drive combo, but when the hard drive failed, I replaced it with a 2TB SSD. So it's the original SSD fused with a new SATA SSD. Since High Sierra doesn't support APFS on fusion drives, this drive is formatted as MacOS Extended (Journaled)
When I try to install Mojave, the following steps proceed ok:
- Download the small macOS Developer Beta Access Utility
- Run the macOS Developer Beta Access Utility which loads a Mac App Store like app
- Download 10.14 beta in the Mac App Store
- Click to Install
- Agree to license
- Select destination for install
Things fail as as I click Install on that screen, once I authenticate myself: "This volume is not a supported Core Storage configuration."