Cannot Change Grub's Default Kernel

[spflanze]

I modified rlaager's procedure to install ZFS that he posted here:
https://openzfs.github.io/openzfs-docs/Getting%20Started/Ubuntu/Ubuntu%2022.04%20Root%20on%20ZFS.html
to customize it to my needs. The latest version of my modifications can be downloaded here:
https://www.mediafire.com/file/2w8mdb96tbzslub/Ubuntu_22.04_Root_on_ZFS_Encryption.odt/file
My modifications are working now to enable booting Ubuntu.

However I find that the default kernel Grub attempts to boot does not work. That default results in the error "No pool imported, Manually import the root pool." followed by an initramfs prompt. Grub's kernel options that do successfully boot have "22.04 LTS" in their names. And so I attempted to change the default kernel to one that does boot. The procedure I followed to change the default is given in Step 7 on this webpage:
https://www.how2shout.com/linux/how-to-change-default-kernel-in-ubuntu-22-04-20-04-lts/

I find this procedure fails to change the default kernel. The changes to the file at "/etc/default/grub" it instructs to do cause the error message:
error: sparse file not allowed
to appear, after which Ubuntu boots normally, provided the right kernel is selected from among the boot options that Grub presents.

Why is this error appearing? How can the default kernel be changed?

[spflanze]

I found my answer here:
https://hamwaves.com/grub-default/en/index.html
This worked.