Please, ask the questions on the forum only in English!
Can the select editor only achieve a level of selection? How can the choice of multiple cascades be realized?
Gantt uses the standard select element for the lightbox section with the “Select” type. There is no built-in way to change it, so you need to create a custom lightbox section where you can return any HTML elements:
I have the following example with the select element that has multiple selections:
You can also use a third-party library. Here is an example with the select2 plugin:
If you need something different, please, describe your question in more detail.