Xcode 11.4.1 support has been added to Cloud Build.
To use Xcode 11.4.1 in Cloud Build, in a build target’s config settings, either configure the Xcode Version setting to “Latest Compatible Version” (to automatically use the highest compatible Xcode version for your Unity project) or explicitly configure the Xcode version to 11.4.1.
If there any issues, please reach out to Support through the support page in the Cloud Build dashboard or email (cloudbuildsupport@unity3d.com)