To supplement @davimacedo comments, you should use Apollo or Relay only if you are set on using GraphQL with the parse server.
Since the Swift SDK you referenced uses REST, you don’t need to do anything special to enable REST on the parse-server, it just works out-of-the box. If you already began writing your client app with the Parse Swift SDK, you should weigh the trade-offs and decode if you want to change it.
Also, you should look for the tradeoffs between the Parse Swift client and the Apollo/Relay clients. The Swift SDK implements most of the REST functionality for the server (that I know of) and designed using the latest Swift and SwiftUI features. Because of this, you will end up finding the Swift SDK easier to use with Swift based OS’s than the other SDKs (if you are familiar with Swift). I don’t know all of the features of GraphQL on the parse-sever, but I would imagine they are not at parity with the REST yet, though Graph may be getting close with all of the development that has been occurring there. I also imagine that with Graph, you have to worry about a lot more on the client side. With the Swift SDK, you don’t think about “REST”, you just code using Parse Objects, Queries, etc. as REST is used under the hood and is agnostic to the developer.