有人知道您在什么情况下需要勾选字体功能框以及如何使用它吗？

Does anyone know in what circumstances do you need to tick that Fonts capabilities box and how to use it?

是的，在iOS 13中是新增功能，您的应用程序可以包含字体，并且可以通过调用CTFontManagerRegisterFontURLs使字体可用于所有用户的应用程序。这称为安装字体。您需要具备执行此操作的能力。您在问题中引用的视频的5:46解释了此功能。观看视频，它说明了所有相关内容。

Yes, new in iOS 13 your app can include fonts and can make them available to all the user’s apps by calling CTFontManagerRegisterFontURLs. This is called installing fonts. You need the capability to do that. The capability is explained at 5:46 of the video you cited in your question. Watch the video, it explains all about this.

您并不需要仅在自己的应用程序中包含和使用字体的权利。

You do not need the entitlement merely to include and use fonts within your own app.