The old Chrome app was introduced as a way for Gmail users to access email offline. However, with the recent Gmail redesign, Google built that functionality directly into the web app.
According to Google, the native solution works better and is easier to use than the old Chrome app.
Google says it will remove the Gmail Offline Chrome app from the Chrome Web store after December 3rd, 2018.
That gives you about two and a half months to transfer over to the native offline functionality.
To access Gmail offline, make sure you enable the feature in settings. Then simply navigate to mail.google.com in a Chrome browser running version 61 or higher. Unfortunately, it doesn’t work on non-Chrome browsers.
Even if you’re not connected to the internet, you should be able to access the last 90 days of email.
Sad as it is to see a feature go, it makes sense this time around. Google is cleaning up its Chrome apps. Removing this app makes sense because its features are built in and work natively with Gmail now.