In order for Analytics to generate reports for your corporate intranet usage, your corporate network must be able to reach the Analytics JavaScript file (analytics.js). Try loading the file in your browser using the following link:
https://googletagmanager.com/gtag/js
If you can reach this URL from your internal network, you can use Analytics to collect data from your intranet. Your intranet must also be accessible through a fully qualified domain name such as http://intranet.example.com. The Analytics JavaScript won't work if your intranet can only be accessed using a domain name that isn't fully qualified, such as http://intranet.