Atlassian's overview of frequently asked questions → https://www.atlassian.com/migration/faqs
What do you mean by End of Sale and End of Support (EOL)? - EOL means that further product development stops and support expires.
Which products are affected by the EOL? - The server products of the self-hosted offerings from Atlassian like Jira, Confluence and others are affected.
Until when can new server licenses be purchased? - New server licenses can be purchased until February 02, 2021.
Until when can upgrades and downgrades for existing server licenses be purchased? - Server license upgrades can be purchased until February 02, 2022.