What are you seeing?
If you try to install Windows 7* using a USB flash drive on an Intel® NUC with only USB 3.0 ports, you might not be able to proceed past the Language Select screen. The USB keyboard and mouse don't respond, so you're unable to select your preferred language.
Why are you seeing it?
The Windows 7 installer doesn't have a built-in driver for USB 3.0. It only supports USB 2.0 devices. Microsoft ended mainstream support for Windows 7. It's unlikely that the installer will be updated to include USB 3.0 drivers.
How to fix it
Refer to the guide below to learn how to use DISM tools to update your Windows 7 image to include a USB 3.0 driver.
Install Windows 7* on Intel® NUC with USB 3.0 (PDF)
Size: 544 KB
Date: June 2018