Something is wrong there that I do not see. I looked again at your Dec 17 support file and I do not see anything that could be causing this. With all MacOS past 13.3, the SoftRAID driver always is loaded, which would be the main reason a file system cannot be created.

While I do not think the problem is softraidtool, lets try "uninstall SoftRAID" from utilties menu, then launch SoftRAID and install again (You will need to reenter your serial number) Then try again.

Also, assuming that does not work, can we try a clean install new System? It does not affect your boot volume, just a second system.

Run Disk Utility
Click on your startup internal
Click + volume
Name/save your volume
Shut down
Startup in recovery mode (hold the power button)
Select Options
Select "reinstall MacOS"
Point the installer to your new volume and install.
Do NOT migrate data, etc. Use the same Admin name.
install SoftRAID. It will run. You can even activate on both systems.

You can delete this second volume at any time. this will confirm whether there is a problem inside your system, or something else, perhaps a problem in the SoftRAID partition maps (which would require a backup/restore to repair, most likely)

Still fails on writing FS to new volume

Only SoftRAID volumes. Lets see what happens when you exempt spotlight. You can enable it later.

Let me ask... just softraid volumes?  All volumes seen by softraid (like other external drives)?

what I think you are missing is unmount ALL SoftRAID volumes, ThunderRAID and Thunderdata and try again.
You may nbeed to A) make sure it is not a Time Machine volume and B) go to Spotlight preferences and "exempt" this volume ( A damaged spotlight index can keep a volume open.)

1. Unmount volume: ThunderRAID via softraid.

2. Softraid crashes.

3. restart softraid.

4. from iterm: diskutil unmountDISK force /dev/disk#

5. ThunderRAID successfully forced offline

6. Create new volume from softraid

7. select six disks (all available)

8. Prefs:  Raid 5; HFS+; Workstation; size 2tb; 16kb stripes; name ThunderDATA

9. System password dialogue

10. FAILS with below screen shot

In your screen shot ThunderRAID is still mounted. Please unmount that volume and try again.

Volume creates, file system fails.

Some process is holding on to your volume, so just manually unount all volumes first.

In general, MacOS security write protects the partition maps on disks with mounted volumes.

SoftRAID adheres to MacOS security guidelines, and when MacOS does not unmount the volume, the application is stuck waiting for a reply, and quits.

I was able to force unmount the other through terminal (smb daemon wouldn't let go of the volume) and then delete the volume.

Now the question remains, how do I create the new volume without Softraid crashing?

thank you!

(happy holidays)