Seems to be a recurring issue. I have a perfect 12 year old Mac running El Capitan but I couldn't use it any more because the xcode didn't match. Then I bought a Macbook Pro High Sierra and now I have the same issue again, I have to buy a new one because I cannot upload to Testflight. Surprisingly I can still compile and deploy to Apple devices direct using provisioning. So it is just a matter of blocked access for testing and distribution. These are hard times, a bit more consideration would be nice.