... directly, you must have Java 9+, including javafx. Oracle and OpenJDK java runtimes no longer include javaFX, and it must be separately installed. Alternatively https://www.azul.com/downloads/zulu-community/ is a JRE that provides a free 'JRE FX' installable that includes java and javafx. Installing it is the easiest way to run KGA on another OS.
Kitchen garden aid is primarily tested on java 15, with javafx 15 on windows. If you notice a bug, especially on another OS please report it so I can fix.