Mac storage basics · Time Machine basics
Can two Macs back up to the same Time Machine drive?
Short answer: Yes — each Mac keeps separate backups on the shared drive, and space is shared, so size the drive for both Macs plus history.
Yes. Each Mac keeps its own separate backups on the drive, and the space is shared between them — when it fills, Time Machine removes the oldest backups. Size the drive for both Macs' data plus room for history.
Adding a separate APFS volume per Mac on the drive can keep things tidy, but isn't required.