The version number 7.6.727.43 points to a release from mid-2017. In the world of Android development, this is considered "vintage." However, versions from this era are often sought after for specific reasons:

: Upon running the executable ( miflash_unlock.exe ), the tool opens two distinct windows: one specifically for signing into your Mi Account and another for the unlocking process and status monitoring.

Ensure the fastboot drivers are installed on your PC. Use a USB 2.0 port if USB 3.0 fails. "Couldn't unlock, please add account in MIUI's settings":

How to Unlock Your Xiaomi Bootloader with MiFlash Unlock v7.6.727.43

: You must have a Mi Account that has been active for at least for the best success rate.