Google announced that they were deprecating support for Chrome Apps over two years ago. Users have not been able to search for the legacy Signal Desktop app in the Chrome Web Store since mid-December 2017, and we officially deprecated the legacy version in October 2017.
Today, the extended support period for the legacy Signal Chrome App is coming to an end. You can still access your existing messages in read-only mode or begin the upgrade process using the built-in data portability option. We apologize for any inconvenience this may cause, and we encourage users to migrate to the latest standalone version of Signal Desktop.
We hope to have the resources to bring Signal to additional desktop platforms in the future. We are hiring: https://signal.org/workworkwork/