Canonical has warned of the imminent end of the five-year update release period for the Ubuntu 16.04 LTS distribution. As of April 30, 2021, official public support for the Ubuntu 16.04 distribution will cease. For users who cannot migrate their systems to Ubuntu 18.04 or 20.04 in time, an Extended Security Maintenance (ESM) program is offered, which extends the release of updates fixing vulnerabilities for the kernel and the most important system packages until April 2024. Access to ESM updates is limited to users with a paid technical support subscription.
Source: opennet.ru