Although we are on Java 13, there are a lot of production installations running with Java 8. As a professional, I developed Java 8 code many times, even these days, and I have to be happy that this is not Java 6. On the other hand, as an open-source developer, I have the liberty to develop Java code using Java 11, 12, or even 13 if that pleases me. And it does.
On the other hand, though, I want my code to be used. Developing a tool like License3j or Java::Geci, which are kind of libraries releasing Java 11-compatible bytecode, cuts off all the Java-8-based applications that may use these libraries.