I hope, that as some point you remove the additional code, that blocks using USB(3) disks as RAID.
He didn't write the code that blocks RAID. That limitation is part of the main project.
There's a reason why this restriction is in place. It's a bad idea, it fails a lot, and most users run without data backup. That's a sure formula for users to return to the forum, asking for support for fixing a broken array that, in many cases, can't be fixed.
If you really want to run RAID, it can be set up on the command line. Thereafter, the array will show up and can be managed in the GUI. But, if you do this, you've been warned.