The only real nut right now is, if you're using the Oracle distributions, only the latest LTS is, essentially, free to do anything with.

Older releases are under their OTN license, which is only for personal and development, but not production.

Again, this only matters if you want an Oracle sticker on your runtime, OpenJDK and the other projects are full boat "do whateva" JDKs.

Note that the previous Java LTS release license reverts to the OTN license one year after the new Java LTS version is published, making it no longer free, assuming you keep up with the security updates. See the license note on the Java 21 LTS version[1].

[1] https://www.oracle.com/uk/java/technologies/downloads/#java2...