I can’t update 1Password 7 version 7.4 from the App Store. I get the error message “Close This App to Update Click continue to quit."
This was indeed an issue in previous versions. It was fixed for quite some time, and now it has cropped up again. I'm sorry for the trouble. Fortunately this should be fixed in the v7.4 update (meaning updates subsequent to 7.4 shouldn't need any special workaround). To get up to v7.4, please try this:
(if you are currently using 1Password from the Mac App Store you may substitute step 6 with reinstalling from the Mac App Store if desired)
Again I apologize for the inconvenience.