Hello Adrien,
As I understand, you want to display terms in the selection of the taxonomy_advanced based on the selected term in the default custom taxonomy box of Meta Box. It is not possible with the field taxonomy_advanced.
I think you can use the field select instead of the field taxonomy_advanced. You can create a custom PHP callback function that returns options for the select field from the selected term. But the options will display on loading, it will not display immediately after selecting the term in the default custom taxonomy box.
Here is an example to create a custom callback function https://support.metabox.io/topic/callbacks-for-the-controls-with-choices/
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