Although I'm no fan of social media (Twitter, Instagram, Tik Tok, etc. etc.), my answer would be YouTube, Blogs and all social media options.
Via titles that equal use cases, and not titles about the product (well, with loads of metadata some somebody looking for TiddlyWiki, or TW, can find these social media jewels.)
So draw folk to the videos and such via problems that need to be solved, or approaches to doing certain things.
For example, thinking of the discussion about notetaking and notemaking.
Instead of a social media something like "Notetaking with TiddlyWiki", draw folk in with something like "Agile Notetaking" (well, some title that draws folk, in the spirit of whatever draws people to viral videos.)
So flood the media with marketing not of the product itself, but of the full breadth and depth of solutions that coincidentally are handled with TiddlyWiki align with whatever plugins when they apply.
As another example, my
Le P'tit Aurèle project. If I were to (when the project is ready) blitz social media with stuff related to that project, it would all be with titles that fall under an umbrella of "Constructing Comprehensive yet User-Friendly Multilingual Dictionaries" (well, something sexier that can go "viral"). And every "post" to whatever social media would have a "by the way, this was built with TiddlyWiki."
If there are a ridiculous number of videos out there on how to do real-world good stuff and they all of the things done happen to be done with TiddlyWiki, I think that would grab some attention.
Something like that ...