(like Adobe Creative Cloud or Font Diner) allow you to install custom font profiles. Install via Settings : Once a font is downloaded through a compatible app, go to Settings > General > Fonts
Technically, you don't need to "download" a separate file if you are looking to use it within the iOS interface. It is baked into the system. For Developers (Swift/SwiftUI): ios 15.4 fixed space -font- download
To use the fixed space feature, follow these steps: (like Adobe Creative Cloud or Font Diner) allow