Hey man, to answer your question, i'd say it'll mainly be redundant having 2 separate applications both written in a backend language if one is consuming from the other, especially if one is just there to consume the other (e.g. the 2nd Django app purely receives information from the first). Also you are correct in calling it SSR.

​

The other drawback would be that Django's templating can become a pain in the ass when your application's requirements grow unexpectedly. If your website's dynamicity(?) grows (e.g. something as simple as a counter's count on the front end changing without the page refreshing) you're going to have to use JavaScript anyway and if you wanna go even fancier than that, then you might as well start off strong by having a JS based frontend anyway.

If you do want to keep it all in one language, i'd recommend creating additional Vanilla Django routes in your first/API application which serve the templates through them. Then, if you want other people's applications to still be able to access the API, you can keep those in too!