When I upgrade my Mac and restart all the windows that were open are gone. Why

First, it makes for a much better upgrade if all apps are quit before you start the process of upgrading your OS (by using the Command key and pressing "Q"). If you do not do that, the OS will generally do that automatically during the upgrade process. Hence, once an app is quit, there is no way for the OS to re-open it automatically. It does not keep tabs on what was open and what was not.

This is especially helpful if the updates includes some tweaks for apps; they cannot be updated without being in a "not-open" state.

And, personally, I never have the same windows re-open automatically as it is good for the computer to be "refreshed" and start anew. I have aliases of all my apps in the dock, so it simply takes one click for me to open the app. Not a great deal of work.

Hello randifromleland,

Thank you for your reply. If you are experiencing this situation only after an update to MacOS it is most likely expected behavior, as all apps must shut down during an update in order for the process to complete. Especially if it is a major update e.g. going from Mac OS Catalina to macOS Big Sur

"Your Mac might restart, show a progress bar, or show a blank screen several times as it installs both macOS and related updates to your Mac firmware." - How

to upgrade to macOS Big Sur

Kind Regards.

Hello randifromleland,

Thank you for posting to Apple Communities. If you would like to keep your windows open after a reboot make sure you tick "Reopen windows when logging back in” when restarting or logging out.

If this doesn't work for an app, it may have its own setting for reopening windows. You can check the app's preferences or documentation for more details.

This also may be expected after an upgrade of macOS depending on details of the update.

Have a great day!

It is indeed very typical for a OS update to ‘refresh’ the computer.