How do I get my iTunes music library into my iPhone 11pro?

It should work with Windows 7 if you download the latest version of iTunes from https://apple.com/itunes. The version in the Microsoft store does not include the needed drivers for syncing.

If all of your music content was purchased from the iTunes store you don’t need to sync it; you can just download it from the iTunes store on your computer. It’s only music from other sources that needs to be synced.

Start here: https://support.apple.com/en-us/HT201253

Follow these instructions to sync iTunes to your phone—>Sync your iPhone, iPad, or iPod using your computer - Apple Support

It might also help if you share with us the error that the computer gave you.