On the Mac, is there a way to track internet usage app-wise. Ideally I would want an app the ability to track monthly usage etc.
Released in 2019 with Catalina, this is what Screen Time was designed for. It gives you a monitoring and control tool to view and manage application and internet usage of you and your child. The one caveat here is that the reports are daily and weekly, not monthly per your requirements.
OpenBSM is a FreeBSD developed auditing framework that track activity down to the individual files accessed. It will create the data, but it will need to be processed using tools like Excel/Numbers or a log processing tool. It’s not for the faint of heart, but it is very powerful. Once you have it set up, it’s auditing capabilities are quite strong.
Full disclaimer: OpenBSM is deprecated and is slowly being replaced my Apple’s new Endpoint Security Framework API, but it’s still included for legacy applications.
Third Party Applications
There are many third party applications available to track/report on macOS usage. Here are just some of the popular ones: