Installing .NET 3.5 offline

I searched on the web and I am trying to follow guides on how to install .NET 3.5 on an offline machine. Steps that I followed:

1. Download official Windows 10 .iso
2. Mount it on D: drive File explorer which shows mounted Windows 10
3. Run dism /online /enable-feature /featurename:NetFx3 /All /Source:D:\sources\sxs /LimitAccess
4. What I get back:

Error: 0x800f081f The source files could not be found. Use the "Source" option to specify the location of the files that are required to restore the feature.

I cannot solve this error, can someone help me out? I thought that feature naming might be bad, I opened mounted Windows .iso and navigated to D:\sources\sxs where I was able to find 4 files:

File explorer showing files