In this case, Apple does not support Windows 10 for your Mac. The other possibility is your Mac Pro is older than the 2013 model. If you did this, then most likely the wrong Windows Support Software was downloaded. My best guess would be you used the Boot Camp Assistant on a Mac of a different year and/or model to download the Windows Support Software. You can post a comment, if I am wrong about this. Your question indicates you downloading the Windows Support Software after installing Windows.

Windows Update may also provide software. Afterwards, additional software can be installed through the Apple Software Update application. Once Widows is installed, additional software can be installed by executing the Setup.exe application included in Windows Support Software. In this case, having the Windows Support Software available to the Windows installer during the installation process may not be necessary. If you have an older Mac and are using the current Windows 10 release, then most likely any required drivers in the Windows Support Software will be already included in the Windows 10 release. This is so the Windows installer can access any drivers included in the Windows Support Software that are not already part of the installation software provided by Microsoft. Unless you have one of the very early Intel Macs, the Windows Support Software is suppose to be available to the Windows installer during the installation process.

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