have similar issue. Need to use offline install to install on corporate win server 2016 standard where direct internet access not permitted.
i have followed all instructions outlined here:
https://learn.microsoft.com/en-us/visualstudio/install/create-an-offline-installation-of-visual-studio?view=vs-2019
i am using the bootstrapper vs_community__246848175.1614096480.exe and renaming it to vs_community.exe
i
i am installing from command line with:
c:\vslayout\vs_community.exe --noweb --add Microsoft.VisualStudio.Workload.ManagedDesktop --add Microsoft.VisualStudio.Workload.NetWeb --add Component.GitHub.VisualStudio --includeOptional
the CNG ley isolation is set to manual and is running.
the install log shows that visual studio is still trying to download files even though this is offline installation and all required files should be in the directory already.
some of the last fails in the log are........
[13a4:00af][2021-07-16T14:07:26] Sleeping 10000 milliseconds before retrying download.
[13a4:00af][2021-07-16T14:07:36] Attempting download 'https://download.visualstudio.microsoft.com/download/pr/47307962-b1d2-4f9f-b026-d43bdd2e4cd5/a764816361f6b75630e74885f2487b00eb45094355e0d195c7a39843610c2e32/Microsoft.PythonTools.LiveShare.Vsix.Resources.ENU.vsix' using engine 'WinInet'
[13a4:00af][2021-07-16T14:07:36] Error in 'InternetOpenUrl' with '12029' - 'Unknown error 12029'.
[13a4:00af][2021-07-16T14:07:36] WinInet error 'UnknownError' Function: InternetOpenUrl, HR: -2147012867, Message: Unknown error 12029 - proxy setting '