Your typographic options can be expanded using font files or a third-party font app.
Font apps are available from the App Store. Fonts installed using this method are available to all apps, including your Affinity apps.
Refer to a font app for instructions on installing its fonts.
OpenType (.otf) and TrueType (.ttf) font files, available from many font foundries, can be installed from within your Affinity app. Fonts installed using this method become instantly available in all your Affinity iPad apps. They are not available in other apps.
The font files need to be stored in a location that's accessible in your iPad's Files app.
The fonts will be instantly available wherever you can select a font in your Affinity app, e.g. when using the Artistic Text Tool or Frame Text Tool.