Answer
Place the .ttf/.otf in Resources/Fonts (MauiFont build action), register it with an alias in ConfigureFonts, then reference the alias via FontFamily. This works consistently across platforms without per-platform font registration.
builder.ConfigureFonts(f =>
f.AddFont("Inter-Regular.ttf", "Inter"));
// XAML
<Label Text="Hello" FontFamily="Inter" />Real-world example A brand typeface is registered once and applied everywhere via the FontFamily alias.