Message in visual studio "This extension is scheduled for install"

I found the solution. There was another VS instance was running.

I closed all my running VS instances & then "VSIX Installer" installed all my extension.

Try, File -> Close instead closing VS by clicking X

Or else, restarting the PC should work according to the warning shown in the window Or else, You can change your settings

Even though you close your visual studio instances, there may be another instance running in background. So make sure you closed all instances in Task manager -> Details. In my case it started to install once i closed all instances.