What version of iOS does Xcode 12.4 support?

Older versions of Xcode can be found by logging into the Apple Developer Downloads page and searching for the version of Xcode you need .12 Tem 2021

Xcode 12.4 includes SDKs for iOS 14.4, iPadOS 14.4, tvOS 14.3, watchOS 7.2, and macOS Big Sur 11.1 . The Xcode 12.4 release supports on-device debugging for iOS 9 and later, tvOS 9 and later, and watchOS 2 and later. Xcode 12.4 requires a Mac running macOS 10.15. 4 or later.

The macOS 10.14. 6 SDK provides support for developing apps for Macs running macOS Mojave 10.14. 6. The SDK comes bundled with Xcode 10.3 available from the Mac App Store.