This was the way I did it in 2021. In that sample, I happened to be linking to icons available on the vendor's websites. If I wanted to re-do it with a link to an image store in WF, then I'd store the image in Documents (or wherever I needed it) to start. Then the URL that you use to link is obtained by right clicking on the file and saying 'Copy link address'. If you open it and try and use the URL in the browser, that won't work. You want a URL that says something like "/internal/document/preview?versionID".
https://experienceleaguecommunities.adobe.com/t5/workfront-questions/text-mode-links-to-external-url...