macOS has an elaborate set of rules determining which types of xattr are preserve during different types of copying, including syncing to iCloud Drive. Here they are in full detail.
APFS
Extended attributes were added to Mac OS X 10.4, and soon supported the quarantine xattr. They have since flourished, and have valuable properties.
Released in Mac OS X 10.5 Leopard on 26 October 2007, it supported Time Capsules launched in January 2008, and in Big Sur could back up to APFS.
Exactly what is the disk shown in the Finder named Macintosh HD, in Big Sur and later versions of macOS? An exploration of the structure of the modern boot disk.
Symlinks are popular but prove fragile when folders get renamed or moved. Hard links don’t support directories and can’t cross volumes. The alias works best overall, but isn’t supported in Terminal.
What if you want to boot your Mac using two or more different versions of macOS, with different versions of APFS? Here’s how to avoid problems.
Update adds two new datestamp fields, and gives decimal seconds in times. Use this app to explore how macOS sets those on files, as shown.
What can cause low copy speeds for very large and possibly sparse files, such as VMs? Causes explained, and tools you can use to discover why.
Most backup apps make snapshots, so why not use those instead of conventional backups? Because of the weaknesses of snapshots, as explained.
Originally two separate apps, they were brought together in Mac OS X, and have survived largely unscathed to Sequoia. Here are some highs and lows to remember.
The Eclectic Light Company 