Hi @jo3 ,
There is currently no modal box shortcode available out of the box with X although there is a lightbox shortcode that you might want to check.
However, you might want to check the Popover/Tooltip which comes with a shortcode that you can use that is native to X.
This shortcode will give you an option to display some tooltips to some texts.
For example, in your contact form 7 form setting you will have the code:
<label> Your Name [extra href="#example" title="Required Field" info="popover" info_place="top" info_trigger="hover" info_content="Please type in your name." ]*[/extra]
[text* your-name] </label>
Hovering over the
* will open the popover box that contains some information about the field like this:
Hope this helps.