While I am not entirely sure what could be causing this, I think your assumption may be correct. I'm not entirely sure which Java version is currently supported by OSBot, but 14+ may not be supported. I'd recommend building against an older, more established Java version (I know that Java 8 is supported, so perhaps start with that?)
Also, ensure that your ScriptManifest annotation is correctly placed and populated - this is required for the script to show up in your selector.
Best of luck, let me know how you get on!
-Apa