Which font formats does iOS support?

The official documentation on this is spotty to say the least. In the article Adding a Custom Font to Your App, Apple states that can use True Type Font (.ttf) and Open Type Font (.otf) files.

In related Apple documentation for setting up a configuration profile on iOS, Apple states that you can use

[a] font file in TrueType (.ttf) or OpenType (.otf) format. Collection formats (.ttc or .otc) are not supported.

Again only True Type Fonts and Open Type Fonts are official supported. Although this document is not directly related to app development. It is further evidence for official support for fonts only extending to .ttf and .otf.

I couldn't find any official documentation for WOFF or WOFF2 support outside of Safari.

As of iOS 7, both TTF and OTF font formats are supported. You can distribute these fonts in your apps, or through configuration profiles (to make them available system wide).

As of iOS 10, both WOFF and WOFF2 formats are supported. Though there's no info about it