Hello Mobau, if hot-swap is “enable” on BIOS, you will be able to remove and install the hard drives connected to the SATA ports.
They act as a regular USB device, just be careful to not disconnect it while it is being used.
Since the hard drive is connected to a SATA port, the safely removing hardware Button, that is usually located on the Task Bar, is not going to appears.
It will come up if the hard drive is plug to an external SATA port.
Here are some pictures that I just took in order to show you how it looks when the HDD connected to an external SATA port.
Mobau, base on your notes, you are still connecting the HDD on an internal port (SATA 4).
The "Safely remove button" will appears when the HDD is connected to an external SATA port or an USB port only.
However, while the hard drive is not being in use, you can connect it or disconnect it without losing your data, even when it is on SATA 4.