com.apple.MobileAsset.LeonardoTextures
is a MobileAsset type with unknown purpose.
It's published in Pallas for the macOS generic audience, and referenced by the Leonardo private framework on macOS, and the "MLRecipeExecutionService" XPC service in Xcode (full path: Xcode.app/Contents/SharedFrameworks/MLRecipeExecutionController.framework/Versions/A/XPCServices/MLRecipeExecutionService.xpc/Contents/MacOS/MLRecipeExecutionService).
The only asset in it contains 243 JPEG images. There are photos of random stuff (no people), and some solid-color images with random text. The purpose of this is unknown. Would need investigating the Leonardo framework itself.
Pallas request
This asset type doesn't require any additional Pallas request fields to obtain the asset list. Sending a minimal request with ClientVersion + AssetAudience + AssetType is enough.