Windows 10 and 11 block unsigned drivers by default. Since 09185 uses legacy drivers, you must:
Move your downloaded .ftf file into the C:/Users/YourName/.flashtool/firmwares directory. flashtool 09185 best
FlashTool version 0.9.18.5 is widely considered the "golden era" release for Sony Xperia enthusiasts. While newer versions exist, this specific build remains the most stable and compatible tool for flashing firmware on older Xperia devices, particularly those released between 2011 and 2015. Windows 10 and 11 block unsigned drivers by default