Of course not. However, OP is a Ubuntu user, as mainstream as mainstream gets. Do you think you are helping a Ubuntu user, who almost certainly does not build his own software, probably doesn't know what a stub kernel is, and has asked about use of an apparently unfamiliar GUI tool to unmount a filesystem, discussing special things a few Gentoo or other advanced users might do as if they were normal for users who choose a mainstream distro?

Sure! Linux will mount whatever /etc/fstab directs it to mount. If required filesystem(s) don't get mounted at boot, boot doesn't complete. For the purpose of getting Ubuntu started, the root filesystem must be mounted, but the ESP partition need not be.

Instead of unmounting after startup, what you could do is include the noauto option in fstab for the ESP partition, then mount it manually whenever some process needs for it to be mounted. Is your memory good enough, and your knowledge of what needs to happen when good enough, to know every time such an event is to occur? Would you know how to recover when you forget?

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I'm pretty sure the image in first post is not about unmounting ESP partition, I believe it is a GUI tool to set noauto in fstab. I may be wrong.

Only if you have an abnormal install. The initramfs and vmlinuz images are in /boot (ext4). The ESP partition is at /boot/efi (vfat) on almost all systems. The boot loader, or what you call the stub kernel, resides in /boot/efi and the kernels reside in /boot.

While it is possible to have /boot on an ESP partition (vfat formatted) and thus not have a separate /boot/efi partition it is abnormal for that to be done. If you have done so, more power to you, but the vast majority of us follow the standard partitioning scheme as setup by the default install.

Although I agree that /boot/efi is not needed and remains unused after startup completes, I disagree with leaving it unmounted because doing so would prevent any update that involved a kernel update from completing. Only if the user was experienced enough to remount that partition prior to the update and remembered to do so could those updates be done.

I doubt the average user could do so and even most of us with years of experience would not favor giving ourselves the extra step of mounting the ESP just to do updates.

Thus I feel your advice to anyone to leave it unmounted is only asking for trouble in the future when users are unable to do updates properly. The cause of those problems would be advice given without forethought of consequences.

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Slackware puts both the kernel and initrd files in its sub-directory in the EFI partition and it is definitely a major distribution, actually the oldest currently existing system. I'm not aware of any other Linux which does this.

Michael Piziak, if you listen to warning GUI disks app is safe I also use it.

It should be noted that Linux does not mount the file systems in /etc/fstab. Those are mounted by mount, as part of the system initialisation by the init process.

What Linux does mount, using it's own functions, is the root filesystem (rootfs). Once init is loaded, it calls mount and remounts / and all other file systems in /etc/fstab.
I believe this is due to the use of elilo rather than grub?