config.ts

interface PluginConfigTypes {
  gtag: {
    trackingID: string
  }
  otherPlugin: {
    test: number
  }
}

type Config<K extends keyof PluginConfigTypes> = {
  title: string
  plugins: K[]
} & Pick<PluginConfigTypes, K>

function createConfig<
  K extends keyof PluginConfigTypes
>(config: Config<K>) {
  return config
}