Qualcomm adds a gbl boot stage in its ABL because it wants to limit OEM's ability. gbl is loaded as an uefi app. it stores in efisp partition you need to flash the efi file into the partition.

The xperable tool is an exploit leveraging CVE-2021-1931 Android Boot Loader vulnerability of fastboot usb interface on Sony Yoshino and Tama platforms, based on Qualcomm Snapdragon 835 (MSM8998) and ...