Sorry I am multitasking. Evidently…
Mounted means that the drive is actively in use by you. A file system is mounted when it is in read/write state.
To alter a drive while it is unmounted, you MAY need to access using your installation media in order to have the drive unmounted in order to make changes to it (True across all OS’s, incl Mac and Windows). So, as an example, if you want to make Certain Changes to the volume or partitions of your Primay Drive, you would need to boot up using your Zorin 15 Installation Disk (or USB) in the Demo mode, then open a terminal, access the drive you wish to alter and you can mount or unmount the drive from the terminal, as well.

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