What is the difference between "detach, pop-up, and safely remove drive" on a USB flash drive/mobile hard drive under Ubuntu?

First, of course we can use umount to uninstall it. You can use the mount command again to reload;
However, if "pop-up"/"eject" is selected, it cannot be reloaded. This is generally applicable to optical drives;
"Safely remove the driver"/"safely remove device", stop rotating the USB flash drive/mobile hard drive and uninstall it automatically;

Difference between "eject" and "safely remove device: The eject is used to pop up the disc, and the safely one is used to pop up the disc, but the disc and the U disk are both movable,
So put them together. If the U disk is not read or written and the sync command is executed before the pop-up, there is no difference between eject and safely.
For the sake of security, we recommend that you use the eject on the CD and the USB disk safely!