If you have the knowledge to modify Flarum core's Mithril components to add your ads, then you should have the knowledge to fix the Ads extension 😇
Flarum is a single page Mithril application, the only way to inject content is using the Mithril API and Flarum's extend methods. Right now it doesn't seem like any developer is actively maintain an extension like the former Flagrow Ads.