[codetrotter]

Having now turned the computer back on I've also confirmed that these flags are indeed now being passed to the kernel when it is booted, as seen in the output of

    cat /proc/cmdline

which shows the following:

    BOOT_IMAGE=/boot/vmlinuz-5.11.0-38-generic root=UUID=4dcba509-efff-4ccc-a099-f919240c767c ro rcu_nocbs=0-15 processor.max_cstate=5 quiet splash vt.handoff=7

And that's the "rcu_nocbs=0-15 processor.max_cstate=5" we added to our GRUB2 config shown right inside of there.