How can I find the date that I upgraded to High Sierra? I have recently discovered that some background processes are no longer running.  They appear to have stopped running around the time that I upgraded to High Sierra (~ 3 months ago).  Is there anywhere that I can find exactly when I applied this upgrade to confirm?
Follow these steps:


Go to Apple > About This Mac
Click on the System Report button
In the lefthand Sidebar scroll down to Software and select the Installations option
In the righthand pane you will see a list of software. Scroll through the list until you see the macOS High Sierra installations (see screenshot below as example):