This version of Xcode isn’t supported in this version of macOS. MacOS 15 Beta
Which version of Xcode are you trying to install on macOS Sequoia 15 Beta ?
From macOS Sequoia 15 Beta Release Notes:
The macOS 15 SDK provides support to develop apps for Mac computers running Sequoia 15 beta. The SDK comes bundled with Xcode 16, available from the Mac App Store. For information on the compatibility requirements for Xcode 16, see Xcode 16 Release Notes.