When I download an extension within Visual Studio 2019 IDE, it downloads successfully and gives a message "changes will be scheduled and that the installs will begin when I close all windows". If I close all the open windows in IDE, nothing happens. Also after a restart, I do not see the extension installed.
changes will be scheduled and that the installs will begin when I close all windows
To close all windows, try going File menu => Exit to close VS instead of clicking the X button.
Here're some other workarounds I found:
1.Download the extension from VS Marketplace and double-click the xx.vsix file to start installing manually.
2.If the popup doesn't show, find the xx.vsix in %USERPROFILE%\AppData\Local\Temp folder, run it there to install. See this.
Of course these are workarounds, however I can't reproduce same issue in my machine. So I guess maybe something is broken in VS or one unknown process interrupts the installation. I suggest we can make sure we're in Admin permission, run a VS repair(or Update VS to latest 16.3.6), and check if one process like cmd(found one similar issue whose cause is about cmd.exe) by task manager...
Hope all above helps if someone meets similar issue :)