MacOS – Can not resize disk image file .dmg

I figured it out!

1. Open Disk Utility.

2. In the left-hand panel, select the disk image you would like to resize (the DMG file), then click the Resize Image button in the toolbar, and then enter the new size. Click Log to ensure that it resized successfully.

3. Click Open to mount the volume. (You may also mount the volume manually by opening the disk image in the Finder.) Select the volume in the left-hand panel. Notice how the volume's Total Capacity is unchanged. This is where you got stuck.

4. Select the disk image again (not the volume). Now there are new tabs available. Click the tab labeled Partition. This essentially allots different partitions of storage space to the disk image. Select the volume you would like to resize and drag the ... draggy thing? or manually enter in a size. Then click Apply. Check the log to ensure the partition was resized successfully.

5. Select the volume in the left-hand panel. Check to ensure its Total Capacity is the correct size.

That's it! Now you can add more files to the volume. Remember to eject the volume when done.

I had the same problem as you, and i searched all the forums and i found that if you turn off FileVault it should work.