Hold control (windows) or command (Mac) when you click a link. That'll open it up in a new tab.
Or middle click with the mouse button is usually a open in new tab shortcut.
We don't have full control over the UI, what it does and doesn't do and that change would be a big change for people that are already used to the "old way" of it. So I think, if it gets implemented by the developers of Lemmy-ui, having it as a toggle-able setting in the user preferences would be amazing!