A new version of the Google+ Android app was released on February 21, 2019. All Android users will need to update to this Google+ Android app immediately to continue using the app. Old versions of the app will no longer be supported. Users can still use Google+ on their mobile web browser at plus.google.com. Note however that on April 2, 2019, Google shutting down the personal version of Google+, a social networking site by Google.
More details here.