Every Apple silicon Mac has soldered storage, so the drive you plug in is the only expansion the machine will ever get. That raises the stakes on two choices most product pages skip: how the volume is formatted, and whether the connection is genuine Thunderbolt or ordinary USB. Get either wrong and a fast drive behaves like a slow one, or refuses to do the job you bought it for.

macOS is opinionated about file systems. Time Machine will not touch an exFAT volume. The Photos library refuses to open on one. NTFS drives from a Windows machine mount read-only. None of that appears on the box, which is why this page starts with formatting rather than with megabytes per second.