grubby is a command line tool to configure bootloader menu entries for Linux. Here are some commands which you may find useful

List Kernels

# grubby --info=ALL | grep ^kernel
kernel="/boot/vmlinuz-4.18.0-553.16.1.el8_10.x86_64"
kernel="/boot/vmlinuz-4.18.0-513.18.1.el8_9.x86_64"
kernel="/boot/vmlinuz-4.18.0-425.3.1.el8.x86_64"
kernel="/boot/vmlinuz-0-rescue-1fd272f10209466d81c89276e275d210"

Check Defaults Loading

# grubby --default-kernel
/boot/vmlinuz-4.18.0-553.16.1.el8_10.x86_64

# grubby --default-index
0

Change Default Loading

# grubby --set-default="/boot/vmlinuz-4.18.0-513.18.1.el8_9.x86_64"

Verify Default Loading

# grubby --default-kernel
/boot/vmlinuz-4.18.0-513.18.1.el8_9.x86_64

# grubby --default-index
1