One idea, (temporarily) deactivate your license and launch 7.5 and see if 7.5 runs.

When you run 7.0 as the workaround, just cancel when asked to update the driver. it will work fine to manage your volumes, and the 7.5 driver will still be installed.

When I upgraded SoftRAID from7.0 to 7.0.1 the monitor screen came up blank and the SoftRAID menus were all greyed out. The RAID array was still accessible.

SoftRAID support advised reinstalling 7.0. I did that, and the SoftRAID monitor screen was restored.

SoftRAID support advised that the problem would be resolved in 7.5. Unfortunately, this is not the case. 7.5 makes the monitor screen go blank once again.

I "fixed" the problem by re-installing 7.0

Also, how would one uninstall a (newer) SoftRAID driver in order to (re-)install the driver that matches an older version of SoftRAID -- as in the case above, when downgrading from 7.5 to 7.0?

Please advise...

You can also do a clean install on the external and use Migration Assistant.

Apple has built in "reinstall MacOS", so they do not think users need a bootable backup. I use bootable second volumes all the time, which is different, you can create multiple MacOS systems on the same volume by creating new volumes with Disk Utility.

"For the reasons noted above, we do not recommend that you attempt to make your backups bootable; we recommend that you proceed with a "Standard Backup" instead. You can restore all of your documents, compatible applications, and settings from a standard CCC backup without the extra effort involved in establishing and maintaining a bootable device."

it seems I will need to install OSX on USB drive and all the apps and mantain as seperate system. I will try to install OSX and see if I can avoid internal SSD wear. But is seems disk cloning doesn't really work with 13.4

Booting from externals has become more difficult. With 13.3 and later, it is easier as a couple of the problems/limitations in MacOS and M1 have been addressed. I thought you could startup from external "clones" now. Check Carbon Copy CLoner and their release notes as if anyone can solve this issue, it is Bombich.

I upgraded to OSX 13.4.1 and SR 7.5 I used SuperDuper! 3.7.5 to clone the disk to external SSD USB and tried to boot, but for some reason I can't boot from that USB disk ( doesn't matter with our without RAID connected) with OSX 12.6.7 I was able to boot from my USB clone (RAID didn't work obviously) and at list I had access to apps/data

I'm able to select USB disk but after selecting it and trying to boot from it, MacMini restarts and boots from internal SSD.

Yes you can.

Before 13.3, you could not load the SoftRAID driver from an external disk, or even Safe Mode. Now you can, with 13.4. So when you upgrade macOS, everything will work as you want.