The most common version matching your description is:
flashtool-0.9.18.2-windows.exe(or a zip archive with that version number)
This is FlashTool for Sony Xperia devices (by Androxyde), version 0.9.18.2. flashtool09182windows top
Step 1: Disable Driver Signature Enforcement (Crucial!) Windows 10 and 11 block unsigned drivers by default, but FlashTool 0.9.18.2 needs them.
Step 2: Run the Installer
Step 3: Install the Drivers
Step 4: Run and Update
This build is often cited as a "top" choice for legacy devices because:
Wait for the green checkmark icon. Disconnect the USB, then power on the device. First boot may take 5–10 minutes. The most common version matching your description is: