/etc/fstab exists solely to stop some error messages from being shown. It's not actually used so you will never see content about drive mounts there. And I'm guessing the command sequence based on the "emmctool" script that's embedded in the Amlogic image. The general principle is that you shouldn't peform change operations on mounted partitions and filesystems and some commands result in auto-remount being triggered so you need to unmount things again before you run the next command. So unmount, grow the parition to 100%, then resize the filesystem to 100%. There's no need for crash helmets as the worst that happens is you mess up something that isn't being used and doesn't already work. You can always start over and have another go.
NB: I'm wondering if an "nvmetool" script might be useful for RPi5 boards.