Please open a command prompt (cmd.exe) as admin and run the following command to install .Net 3.5:
DISM /Online /Enable-Feature /FeatureName:NetFx3 /Source:d:\sources\sxs /All /LimitAccess
(replace D: with your mounted Win10 ISO)
In some environment, DISM fails to fetch the file (Proxy, network policies). The DISM command takes the files from the DVD and you’re fine.
