I am not sure if one of those options is what you are looking for. Both still show not only the text but also, for example, the post author.
You can Print a topic as a PDF by adding /print to the URL. For example, https://meta.discourse.org/t/expand-composer-button-on-mobile/296469 is printed like this:
https://meta.discourse.org/t/expand-composer-button-on-mobile/296469/print
Discourse also offers a raw view.
Therefore, you can replace the /t/topic-title/ in the URL with /raw/. If there is a post number at the end of the URL, you see the raw of that post; otherwise, you see the one for the whole topic. However, the author and the post date also appear in the raw view.
The topic looks like this in raw view: https://meta.discourse.org/raw/296469/