What disk block allocation scheme is used by APFS in macOS?

APFS uses GUID Partition Table (GPT) as the partition scheme, or, as how you called it, the disk block allocation scheme.

The GUID Partition Table (GPT) is a standard that applies to the layout of partition tables of a physical computer storage device, such as a hard disk drive, a solid-state drive, or a USB thumb drive. Using universally unique identifiers, this partition scheme is also known as globally unique identifiers (GUIDs).

If you choose GUID Partition Table (GPT) as the partition scheme for your drive, it means one or more APFS containers are included in the GPT scheme (partition type GUID is 7C3457EF-0000-11AA-AA11-00306543ECAC). Each container contains one or more APFS volumes and each APFS volume shares the container's allocated space together.

The GUID Partition Table (GPT) is supported by all current operating systems, no matter you are running a Windows PC or a Mac device. Some of the macOS and Microsoft Windows on the x86 architecture devices even support booting from GPT partitions only on systems with EFI firmware.