I’d love to have SF Symbols renderable in AR! It actually works with RealityKit on macOS by copy and pasting the symbols, but not available in the system font on iOS.
You may want to check with the SF Symbols team to confirm this is not possible yet, and also file a feature request on feedback assistant.
A bit of a hack solution but you may be able to get this work via drawing the Symbol to a CGImage and passing that image in as a texture.