No need to convert the string to a link. If the string contains a valid url, it will open a browser and show that website.
To make the string accessible and clickable on a page, add the widget ‘Link button’.
The easiest way to do this is to use a button with type "Link" and set the string attribute as the URL attribute.
If your use case is a bit more complicated, for example, when you need to display the link as part of a text, things like the "Rich-Text" Widget might help.