问题：
Project WARNING: Qt has only been tested with version 10.15 of the platform SDK, you're using 12.3.
Project WARNING: This is an unsupported configuration. You may experience build issues, and by using
Project WARNING: the 12.3 SDK you are opting in to new features that Qt has not been prepared for.
Project WARNING: Please downgrade the SDK you use to build your app to version 10.15, or configure
Project WARNING: with CONFIG+=sdk_no_version_check when running qmake to silence this warning.原因：
Xcode和Command_Line_Tools的更新导致SDK版本过高，从而SDK版本不一致
解决方案1：
在pro文件中加入以下两行语句：
QMAKE_MACOSX_DEPLOYMENT_TARGET = 10.15
CONFIG += sdk_no_version_check即强制使用10.15版本的SDK，并忽略版本检测
然后 右击项目-->重新构建
解决方案2：
在终端terminal运行以下命令 以删除原来的qmake系列文件
find ./ -iname '*.qmake.*'然后，重新新建项目运行
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