A Microsoft open-source app platform for building Android and iOS apps with .NET and C#.
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I am using macOS catalina 10.15.7 on win pro 10 and visual studio 2019.
I wonder which version of xcode should I install in catalina?
That's a question for Apple not for Microsoft.
Per https://developer.apple.com/support/xcode/ , XCode 12.4 is the latest version that runs on Catalina. You will need a newer version to submit to the App Store.