The primary partition cannot be shrunk due to immovable files (paging file, hiberfil.sys, or MFT fragment).
You should see:
The name "8 - OEM Recovery Partition Creator v1.3.10B" refers specifically to the entry numbered "8" within the legendary "Jiewei’s Recovery Tools" suite. While the suite contains various utilities for BIOS modification and recovery, entry #8 is dedicated to the creation of Original Equipment Manufacturer (OEM) recovery partitions. 8 - OEM Recovery Partition Creator v1.3.10B