It seems that at about macOS Sequoia 15.1.1 and later external boot volumes might get the following disk image which annoyingly "litters" the Disk Utility list when booted to such volume (in the screenshot below the Mac was booted from an external macOS 15.2 volume that lists a snapshot):
Creedence11M6270.SECUREPKITRUSTSTOREASSETS_SECUREPKITRUSTSTORE_Cryptex
That .dmg is at (visible or in some setups invisible):
/System/Library/AssetsV2/com_apple_MobileAsset_PKITrustStore/purpose_auto/6dd55b0d06633a00de6f57ccb910a66a5ba2409a.asset/AssetData/Restore/SECUREPKITRUSTSTOREASSETS_SECUREPKITRUSTSTORE_Cryptex.dmg
It seems for some users that .dmg is somehow auto-mounted to the Desktop, sometimes multiple times. But I have not seen that behavior.
That .dmg seems to need more than 'sudo rm' if the user wants to delete it.
For example in my setup (Mac mini 2018 Intel, macOS 15.2, Carbon Copy Cloner 7.0.4):
The internal macOS 15.2 volume that is updated incrementally at every step from a cleanly installed 15.0 to 15.2 does not have that folder or .dmg. But if I use CCC 7.0.4 to make a bootable clone from it to an external volume, boot to it, then that folder and .dmg is somehow generated and visible in Disk Utility list.
On the other hand, if I use CCC to clone an existing old macOS 15.1 bootable clone disk image to a "real" volume, and boot it, then that enclosing folder and .dmg does not exist. But after updating that volume to macOS 15.2 it is generated.
Silicon Macs use the internal disk also for the initial boot sequence to external disks so maybe it is related to this issue also on Intel Macs?
I have decided to ignore this cosmetic issue.
