is widely considered a "sweet spot" version for Sony Xperia enthusiasts, particularly for those working with 2014-era and older devices like the Xperia Z2 or Z3.
Flashtool 0.9.18.5 is legendary for reviving “hard bricks.” If your Xperia is stuck in a bootloop, soft-bricked, or showing only a flashing red LED:
Flashing
Flashing with version 0.9.18.5 is a straightforward, albeit delicate, process: Flash Xperia devices with Flashtool - The FreeBSD Forums