Microsoft .net 3.5 keeps popping up and wont install

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.NET Framework 3.5 installation errors - Windows ClientMicrosoftLearn

Fix - Use Windows installation media

You can use the Windows installation media as the file source when you enable the .NET Framework 3.5 feature. To do this, follow these steps:

1. Insert the Windows installation media.

2. At an elevated command prompt, run the following command:

note Source:D: maybe different depending on PC. After you plug in the media look what drive it is in

Dism /online /enable-feature /featurename:NetFx3 /All /Source:D:\sources\sxs /LimitAccess