This was always meant as a simple workaround when Joomla was inserting absolute URLs to images and internal links in the articles, complete with the protocol (http:// or https://), and when third party extensions would include CSS and JS files using absolute URLs always using the http:// protocol. Both of these would cause the site to show a mixed content warning under HTTPS. This feature simply replaced all instances of http:// with https:// in Joomla's output. However, this would also apply to namespaces used in inlined documents, e.g. SVG files, which renders them invalid. In the past 12 years Joomla has stopped storing absolute URLs and third party extensions have stopped using absolute URLs too, rendering this feature obsolete.
If necessary, you should audit your site's links to ensure they are either relative links (when you are cross-linking pages internal to your site), or using HTTPS where appropriate.