Which partitioning scheme is accessible by all Macs, even if not bootable?

The correct choice is MBR (Master Boot Record) because it is a partitioning scheme that is universally recognized by different operating systems, including those running on all types of Macs. While MBR has limitations, such as a maximum size of 2 TB per partition and support for only four primary partitions, it is broadly compatible and allows access to the data on the partitioned drives.

Though other options like APM and GUID are also used in Mac environments, they are either specific to certain Mac configurations or are designed primarily for bootable volumes. APM is mainly found in older Macs and is not commonly used in newer systems, while GUID is tailored for use with Intel-based Macs and provides advanced features necessary for booting macOS but may not be readable by all systems, particularly older ones.

FAT32, while accessible by various operating systems including macOS, is not a partitioning scheme in the same way as the others listed. It is a file system that can be utilized on an MBR partition but does not serve the same function as a partitioning scheme. Therefore, MBR stands out as the most compatible option available across all Macs.