Mac: MacBook Pro 16-inch (Intel, 2019) macOS: Tahoe 26.5.1 I'm trying to determine whether this is expected behavior or a bug. Setup I purchased a new 2TB SSD to use exclusively for Time Machine. Before configuring Time Machine, I manually erased the SSD in Disk Utility and formatted it as: APFS (non-case-sensitive) Encrypted I specifically did not choose APFS (Case-sensitive). What happened After selecting the SSD as a Time Machine destination and allowing macOS to prepare the disk, I later checked the volume information and found: File System Personality: Case-sensitive APFS and: APFS Volume Disk (Role): Backup Name: Brad Mac Backups SSD (Case-sensitive) The volume appears to have been converted to a dedicated APFS Backup volume and is now reported as case-sensitive. Additional observations After backups complete: tmutil status reports: Running = 0 indicating Time Machine is no longer running. However, Spotlight processes (mds and mds_store) continue accessing the backup volume for many hours afterwards, preventing normal ejection of the SSD. Using: sudo lsof | grep "/Volumes/Brad Mac Backups SSD" shows Spotlight processes holding the drive open. Finder's "Force Eject" works successfully. Questions Is it expected behavior in macOS Tahoe for Time Machine to create a Case-sensitive APFS Backup volume, even when the destination was originally formatted as standard APFS? Has anyone else observed a Time Machine destination changing from APFS (non-case-sensitive) to APFS (Case-sensitive) during setup? Could the case-sensitive APFS format be related to Spotlight continuously indexing the backup volume and preventing normal ejection? Relevant Output diskutil info disk3s2 returns: File System Personality: Case-sensitive APFS and: diskutil apfs list shows: APFS Volume Disk (Role): Backup Name: Brad Mac Backups SSD (Case-sensitive) Mount Point: /Volumes/Brad Mac Backups SSD 1 Any insight would be appreciated, as Apple Support was unable to explain why the backup volume became case-sensitive.