There are two main branches of JDKs, OpenJDK and Oracle JDK (both maintained by Oracle).

Builds for the former are open-source but only updated for 6 months after each release, while the latter is under a commercial license with 3+ years commercial long-term support for some versions.

Projects like Eclipse Temurin (Adoptium) bring the LTS to OpenJDK. The underlying code is entirely open-source, so there is no licensing trouble.

Hence, if you want to download OpenJDK, it's important to do it from Adoptium, as you won't get updates on java.net after a while.