Starting with the version 7.8, the UI Designer now includes a Modal container among the out-of-the-box widgets. As the documentation explains, the modal container can be used to create a pop-in window; it can then be opened with a button by choosing Open modal in the button's Actions property.
However, you may wish to be able to open your modal container with a widget other than a Button. Well, here is how you may easily manage to do so.
If you use several JDK versions on your computer, you might want to force the Studio to use a specific version. You can have several versions of the JDK installed in your system at the same time, for example: the latest Oracle JDK 11.0.6 set as your system's default version, for all applications to use (except the Bonita Studio 7.10.4) OpenJDK 11.6 (jdk-11) for the Bonita Studio 7.10.4.