After upgrading to MacOS 15.6 (24G84) I have numerous residual files sitting in a drive called "Update"

Last login: Wed Aug 20 14:24:17 on console

mac@Macmini ~ % diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk0

1: Apple_APFS_ISC Container disk1 524.3 MB disk0s1

2: Apple_APFS Container disk3 994.7 GB disk0s2

3: Apple_APFS_Recovery Container disk2 5.4 GB disk0s3

/dev/disk3 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +994.7 GB disk3

Physical Store disk0s2

1: APFS Volume Macintosh HD 11.3 GB disk3s1

2: APFS Snapshot com.apple.os.update-... 11.3 GB disk3s1s1

3: APFS Volume Preboot 7.1 GB disk3s2

4: APFS Volume Recovery 1.0 GB disk3s3

5: APFS Volume Data 852.7 GB disk3s5

6: APFS Volume VM 15.0 GB disk3s6

/dev/disk4 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *4.0 TB disk4

1: EFI EFI 209.7 MB disk4s1

2: Apple_APFS Container disk5 4.0 TB disk4s2

/dev/disk5 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +4.0 TB disk5

Physical Store disk4s2

1: APFS Volume TimeMachine 913.9 GB disk5s2

/dev/disk6 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *5.0 TB disk6

1: Apple_HFS WD Elements 5.0 TB disk6s1

(free space) 135.2 MB -

/dev/disk7 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: FDisk_partition_scheme *1.0 TB disk7

1: Windows_NTFS LACINEMA 1.0 TB disk7s1

mac@Macmini ~ %

WhatSize has been regularly updated all these years. My version is Version 8.2.3 (8230), updated July 27, 2025.

I think I panicked for no reason at all, this volume must be part of the System which started to show in the Finder sidebar although I don't understand why it is there. Solved.