Building squashfs image using a modified device tree

I'm very new to the image building process, so please excuse my maybe stupid newbie question. :grin:

I have this device using MT7620a + MT7610e EVB, the same as in this thread:

If I flash the initramfs image, it works well. Using the squashfs image, the kernel boot fails with these error messages:

[    0.766222] VFS: Cannot open root device "(null)" or unknown-block(0,0): error -6
[    0.781014] Please append a correct "root=" boot option; here are the available partitions:
[    0.797592] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    0.814958] Rebooting in 1 seconds..

Reading the linked thread it gets clear that the device uses a different partition table than the default image. Modifying the corresponding dts file seems to solve the problem. I found the file, tinkered a bit with it and built some different images, but none of them worked. I sadly don't know enogh about this topic.

Could someone please explain to me what @dbrb2 did, mentioned in this post?

Thank you very much in advance.