100s of ways.

Start by reading the book "Free" by Chris Anderson for a history of old style + new style approaches.

Then hire a bunch of smart people for an hour each to tell you how they'd monetize free for your project.

In fact searching for - how to monetize free apps - returns 25M results for me, so likely this search might be a good starting point for you.

Also study Podcast Monetization + Radio Show Monetization, both of which have been monetizing audience free content for years.