Hi @emiljanQ3,
KNIME AP currently requires java 17 and will not yet work with newer java versions. Your error message indicates that you used a java 22 sdk (Class File Versions - javaalmanac.io). You need to set the execution environment to JavaSE-17 to ensure the compiling JDK creates the right bytecode:
I recommend you to use maven to build your extension, it is much more robust than using the update site building mechanism from eclipse directly.
Please take a look at this template repository on how to do this:
best,
Gabriel