Canonical has warned that the five-year update period for the Ubuntu 16.04 LTS distribution will soon expire. Starting April 30, 2021, official public support for Ubuntu 16.04 will no longer be available. For users who do not have time to transfer their systems to Ubuntu 18.04 or 20.04, as with previous LTS releases, the ESM (Extended Security Maintenance) program is offered, which extends the publication of updates that eliminate vulnerabilities for the kernel and the most important system packages until April 2024. Access to ESM updates is limited to paid support subscription users only.
Source: opennet.ru