DropDMG currently doesn’t work on macOS 11 Big Sur.
DMG creation fails with the following error:
*** Building the disk image failed because DMG Canvas could not unflatten the disk image.: hdiutil: unflatten: verb not recognized Usage: /usr/bin/hdiutil <verb> <options> <verb> is one of the following: help attach detach eject verify create compact convert burn info checksum chpass erasekeys imageinfo isencrypted makehybrid mount mountvol unmount plugins resize segment pmap udifderez udifrez
Indeed, looking at the man page of hdiutil on Big Sur reveals that flatten and unflatten are not among the supported verbs anymore.
Here’s an excerpt from the man page:
hdiutil uses the DiskImages framework to manipulate disk images. Common verbs include attach, detach, verify, create, convert, and compact. The rest of the verbs are currently: help, info, burn, checksum, chpass, erasekeys, imageinfo, isencrypted, mountvol, unmount, plugins, udifrez, udifderez, resize, segment, makehybrid, and pmap.
The verbs are still present in hdiutil on Catalina but the man page warns they’re both deprecated.