flutter build ios-framework --output=some/path/MyApp/Flutter/

Link and embed the generated frameworks into your existing
application in Xcode.  There are multiple ways to do
this—use the method that is best for your project.

Link on the frameworks

For example, you can drag the frameworks from
some/path/MyApp/Flutter/Release/ in Finder
into your target’s Build
Settings > Build Phases > Link Binary With Libraries.

In the target’s build settings, add $(PROJECT_DIR)/Flutter/Release/
to the Framework Search Paths (FRAMEWORK_SEARCH_PATHS).