On the latest Mac system, you can't open the dmgpart segmented file, and you can't select all, and you can open all on the previous system, but now you can't!

DropDMG
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1

On the latest Mac system, you can’t open the dmgpart segmented file, and you can’t select all, and you can open all on the previous system, but now you can’t!

2

Is this related to DropDMG or are you referring to the Mac Finder? What does “select all” refer to?

I’m not exactly sure what you mean because I don’t think .dmgpart files were openable before. Normally, you would mount a segmented disk image by opening the first part, whose name ends with .dmg.

3

I am facing the same problem in my M1 machine. Even if I double click the first part .dmg file. I got:
The disk image couldn’t be opened
The operation couldn’t be completed. Operation not permitted

I got the same error before, in my Intel machine. However, I could still open it by selecting ALL segments and then open them at the same time. I will then able to open and read the content. However it doesn’t help in my M1 machine by selecting and opening all segments in one time.

4

Which version of macOS are you using? Have you checked the file permissions of each part file? What happens if you try to verify the disk image with DropDMG?