Select “Flashmode” (not Fastboot). A new window will appear.

Flashtool 0.9.22.3 also includes a Fastboot interface for unlocking the bootloader, flashing kernels (boot.img), and TWRP recovery.

Newer versions of Flashtool exist (up to 0.9.35.x as of late updates), but 0.9.22.3 remains highly sought after for several reasons: