The question is, why I got an empty set in preview mode ?(as well as in Matomo Tag manager)
At the same time, I tried to retrieve the data through tag custom variable, what should i input for get the mtm.clickElement details ? (i.e. src, href)
It may show as empty but actually the element may work. Could you check whether the element is really empty or not, in the datalayer by calling MatomoTagManager.dataLayer.get('mtm.clickElement') in JavaScript?