No file system could mount root

Trying to install openWRT in virtualbox following the guide.

I downloaded the latest stable release 22.03 and continued. However I can only get a boot loop. After I recorded the screen I found the error was sth:

No file system could mount root: tried ext3, ext4...
Kernel panic..

But when I used the 19.07 release it's working. I later tried also 21.02 and got the same error (boot loop)

Edit: All the images used were combined-ext4.img.gz version (as in the guide) instead of combined-squashfs.img.gz