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sudo awk -F\' '/menuentry / {print $2}' /boot/grub2/grub.cfg
Check if all the kernels listed in order and properly set the version (latest on top) if not generate config again.
grub2-mkconfig -o /boot/grub2/grub.cfg
Redo the previous step and confirm all are listed as expected.
grub2-editenv list
The first item in the list denote entry '0'
grub2-set-default 0
This will set first entry in list to default