Knowing how the taxonomy field works, there would be some problems in doing this. These have to do with the way that the terms are sorted as well as the ability to load/save terms and to create new terms. None of this would work correctly if you could pick multiple taxonomies.
My suggestion would be to look into using a different field type to accomplish what you want to do. For example, you could build a select field and dynamically populate the choices https://www.advancedcustomfields.com/resources/dynamically-populate-a-select-fields-choices/. There is also the possibility of building a custom field type https://www.advancedcustomfields.com/resources/creating-a-new-field-type/
You could also submit your request here https://support.advancedcustomfields.com/new-ticket/.
