Disk Image Mounter Not Working

hdiutil should work in Monterey (see Terminal help text below).

I've had no trouble mounting disk images with Monterey. You could try booting in Safe Mode to see if this makes a difference. Also, you can run Terminal or the Disk Utility from a bootable installer image to see if the disk image mounts. If the bootable installer for Monterey doesn't mount the image, you could also try this approach with an installer for Big Sur or Catalina to see if there's any difference.

- Pie Lover

Are you trying to restore a Volume from an earlier Disk Image? I had some issues creating a Disk Image where the source folder has to be stored on the system data volume. If your disk image is stored externally, try copying it to the system volume, mounting it, and then try restoring from the disk image to the desired volume.

For comparison, below is the Disk Utility info for a mounted disk image (created using the Disk Utility). I noticed that mine is formatted as an APFS volume with an APFS file system. If needed, I believe that the Disk Utility has some disk image conversion options.

- Pie Lover

What specific DMG?

If you go to Finder, select the DMG and then right click and select Get Info what does that show?

Can you open other DMGs?

I just bought both a used MacBook Pro (Early 2015) with Big Sur, and a Mac mini (M1 2020) with Monterey and I am running into the exact same problem. I have 70 disk images of CDs saved on our NAS that five of our homeschooled kids use extensively for their math software. We do this because all of the kids will eventually use all of the disks, and rather than have them putting the disks in and out and eventually destroying some or all of them, I imaged them all and put them back in the package.

So everything was working fine with two iMacs, one running Sierra and the other running High Sierra. Bought the newer computers and neither of them will read the images reliably now using Big Sur or Monterey. In fact, Big Sur doesn't seem to open ANY of them. Monterey seems to mount some of them. No rhyme or reason yet as to what is different on the Monterey (Mac mini) machine.

I have gone to my old reliable Mac Pro (Early 2009) running El Capitan and they seem to mount just fine there.

I offer all this not just to "...me too", although you can put an explanation point on that as well, but also so that Ashley8098 might see if the images will mount on another machine, if she has access.

I downloaded and mounted the Dropboxinstaller DMG file without problems. Once mounted, I can double-click on the mounted disk which launches the installer (see below). I didn't try to actually install DropBox.

- Pie Lover

Maybe I don't understand but the Disk Utility isn't able to install an application (using restore). Try opening the mounted disk image to install.

- Pie Lover