__typename as readonly field

[kencanak]

I am trying to migrate from apollo code gen, while all the types being generated nicely, I noticed that the field __typename is not marked as readonly field. any idea how to make it as readonly field only?

my config setup:

        nonOptionalTypename: true,
        preResolveTypes: true,
        namingConvention: "keep",
        useFlowReadOnlyTypes: true,
        useFlowExactObjects: true,
        mergeFragmentTypes: false,
        flattenGeneratedTypes: true,
        exportFragmentSpreadSubTypes: true,
        dedupeOperationSuffix: true,

plugins:

flow