It sounds simple, but the iPhone 7 is sensitive to power fluctuations during firmware loads. Use an and plug it directly into the motherboard (the back of the PC) rather than a USB hub.
This is the specific hardware board configuration (CPID) for that device.
Release the button but keep holding Volume Down for another 5 seconds.
Don't rely on the software to "auto-detect" the firmware. Go to a trusted source like . Select iPhone .