I've been developing using Xcode (10.1) on an iMac (21.5-inch, Mid 2010) running macOS High Sierra (Version 10.13.6).
The last time I updated my app on the App Store, I got a warning:
ITMS-90725: SDK Version Issue - This app update was built with the iOS 12.1 SDK. As of June 30, 2020, updates to apps for iPhone or iPad must be built with the iOS 13 SDK or later.
I read that iOS 13 SDK comes bundled with Xcode 11.
But when I go to App Store → Updates, I don't see anything to update on my iMac. I can expose "1 incompatible Update", which is "Xcode Version 11.5", which should include iOS 13 SDK. This is what I would need in order to keep updating my app on the App Store, but it's "incompatible".
The problem seems to be confirmed by this compatibility chart. It looks like my current OS is as far as Apple is willing to take me on my current hardware (High Sierra, but not Mojave or Catalina).
My question is, is there any work-around that would allow me to use my current machine, but build using iOS 13 SDK?
I power-on this machine on three or four times per year, in order to make a tweak to the application, and then upload the new app to the App Store. I really don't need or want to buy another computer just to do this.