I'm having the same problem. I filed a feedback: FB9958483 (Xcode Cloud cannot create workflow with Xcode 13.3)

So, this is definitely some kind of bug in 13.3. You can see some Xcode assertion getting thrown in the console logger. I've added some more information to the feedback I posted in the other answer (which I now realize should have been a comment). I did find a workaround, however. If you re-download and install Xcode 13.2.1—I installed it as Xcode_13.2.1, renaming it from the default Xcode so that I could keep 13.3 installed for iOS 15.4 devices—you can create new workflows there. It even lets you pick Xcode 13.3 as the target build system in Xcode Cloud and everything gets set up correctly. Then, you can close 13.2.1 and open 13.3 and you will see your Xcode Cloud workflows. You can run them, edit them, download assets, etc all like normal once they're created. If you have to create another workflow, just open 13.2.1 again. Kind of annoying, but not that bad as workarounds go. You can download older versions of Xcode under Downloads then More and scroll down, or get it directly here (assuming this forum lets me post the link): https://download.developer.apple.com/Developer_Tools/Xcode_13.2.1/Xcode_13.2.1.xip

I still see it. Did you accidentally choose a multiplatform app? That's the default now, and that uses SwiftUI since that's their multiplatform solution. If you want to do something like iOS w/ Catalyst, you need to pick an iOS app (or macOS or whatever) and then you'll see the drop downs you're expecting.