Start with default generated template

templates/field/link-formatter-link-separate.html.twig

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+{#
+/**
+ * @file
+ * Theme override of a link with separate title and URL elements.
+ *
+ * Available variables:
+ * - link: The link that has already been formatted by l().
+ * - title: (optional) A descriptive or alternate title for the link, which may
+ *   be different than the actual link text.
+ *
+ * @see template_preprocess_link_formatter_link_separate()
+ */
+#}
+<div class="link-item">
+  {%- if title -%}
+    <div class="link-title">{{- title -}}</div>
+  {%- endif -%}
+  <div class="link-url">{{- link -}}</div>
+</div>