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.