This support ticket is created vor 5 Jahre, 5 Monate. There's a good chance that you are reading advice that it now obsolete.
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The documentation says that you need to specify the html option as true if you want to be able to use html within the title that is used for the tooltip content: hidden link
I looked at the solution in that stackoverflow article and effectively copied and pasted it into my WordPress site and it worked, so then I modified it a little to use a types shortcode to output a thumbnail of an image field for the tooltip content, and that worked okay.
I ended up with this:
<p>An <dfn title="onomasticon"><button disabled class="dfn-tooltip"><p>[types field='logo' title='%%TITLE%%' alt='%%ALT%%' size='thumbnail' resize='proportional'][/types]</p></button></dfn> is not a dinosaur.</p>