Repartitioning drive

First question - what is the FORMAT of the drive?

If it is APFS, in Disk Utility you need to do View > Show All Devices before proceeding with partition management; and you partition the top level device, not any of the indented containers showing within the device.

Also, if you want to expand your partition, the space you expand into needs to be actually free, unused, unpartitioned space and it needs to be after & adjacent to the partition you want to expand.

And it needs to be said again & again ... make sure you have a reliable backup of all your data before doing this kind of surgery on your system.

And FWIW, never use any third-party partitioning or formatting app to do this. You are almost guaranteed to corrupt the drive if you do so.

I hesitate to mention it, but there are third party partition utilities available for this purpose. I've heard horror stories about lost data in some cases and I wouldn't consider using one, unless the data is backed up on a different drive. ymmv

The best thing to do is save the data elsewhere, erase and partition the drive as desired, then add your data to it.

Hi,

Click the + button to add a partition.

In testing on an external drive on my Mac, it's not possible.