If you spend a lot of time using an iPhone or iPad, and you happen to have a large collection of apps and games, chances are iOS 11 thinned your collection somewhat. This was due to Apple ending support for 32-bit apps. Sadly, it’s not viable for every developer to update their apps, so some simply don’t work on iOS 11.
It looks like a similar situation will affect the Mac at some point. At WWDC 2017, Apple said all apps and games submitted to the Mac App Store from January 2018 will have to be 64-bit. Updates to existing apps must comply by July.
To check your apps, go to > About This Mac, click System Report, and select Applications in the sidebar. Click the “64-bit” header to sort the list so 32-bit apps are at the top, take notes, then contact relevant developers to see if they plan to introduce 64-bit versions for the next macOS.