I just installed the newest Eclipse and e(fx)clipse, but it didn't change anything - I have no idea why javafx imports are not resolved.
Sorry I can't provide more proves I tried to solve it, but I just think (and remember it was I like that before) installing it and restarting Eclipse should be sufficient.
The purpose of e(fx)clipse is not to resolve JavaFX imports. If using Java 11 or higher, you have to add the JavaFX dependency yourself because JavaFX has been removed in Java 11. See Java 11 release notes:
JavaFX is no longer included in the JDK. It is now available as a separate download from openjfx.io.
See: Getting Started with JavaFX 11
e(fx)clipse offers as a runtime e. g. a way to build JavaFX OSGi/Eclipse-based applications and provides tooling for JavaFX, e. g. to edit FXML files.