Hi everyone, first post here.
I just wanted to give you my 5 cents on this topic and how I partially* solved it (running a Mac Pro 5,1 from 2012).
I upgraded to 6.10 today and after the reboot I was stuck with the same error message
VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
Please append a correct "root=" boot option;
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
I tried the solutions mentioned in other posts like adding /root/sda, only copy the bz* files and what not, nothing worked. Reformated the USB-stick and ran diskpart to clean it and all that, still no luck. I tried the same with 6.9.2 (what I was running before the update) and still got the same error message. I did all this from Windows and figured I might as well could try the USB creator tool from my MacBook, and lo and behold.. it worked..
So what I did was the following:
Downloaded and ran the Unraid USB Creator tool
Chose "Stable" branch and version "6.9.2"
Clicked "Customize" and checked the "Allow UEFI Boot" and entered my IP and all that.
Chose my USB-Stick and hit "Write"
After the tool was finished I copied the config folder from my backup zip file (the one created in Unraid) to the USB-stick and replaced all files
Started the terminal and ran the script "make_bootable_mac" in the root directory of the USB-stick
It booted up just fine and everything worked as it used to..
Some final words; Yes, I know, not everyone got a Mac laying around (I don't blame you) but something seems different between the tools on the different platforms.
*I only managed to get 6.9.2 running, but I will try the same method tomorrow with 6.10.2 and hope for better results.