Yes, this is strange. There is no way I can see to display the contents of the URL field using Elementor, I can only use it as the link url for some other text or field. Strangely limiting. And also makes it harder to not display if the URL field is empty. Will try just switching to using a text field for urls.
ACF 5.9.5
Elementor 3.1.4 (+ elementor pro 3.1.1)