Hello,
I suggest that check if .net frame 3.5 and 4.8 has been installed in Server role and feature.
If the issue still insists, i suggest that specify a source, such as the installation media. Mount the Windows Server 2016 ISO to install windows defender feature.
[FIX: Windows Defender Feature Installation Failed–Source files could not be found in Server 2016 (Solved) - WinTips.org](https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.wintips.org%2Ffix-windows-defender-feature-installation-failed-source-files-could-not-be-found-in-server-2016%2F&data=05%7C02%7Cv-xiuyunlian%40microsoft.com%7C668ff502838e448fe75b08dc4c9cd07e%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638469483631847957%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C%7C&sdata=1A%2F3v%2BLpUkVZEyYaMH%2B9glV0KEphFQoG1qMvfYgeC%2Bc%3D&reserved=0"Original URL: https://www.wintips.org/fix-windows-defender-feature-installation-failed-source-files-could-not-be-found-in-server-2016/. Click or tap if you trust this link.")
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Best Regards,
Hania Lian
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