Another TiddlyWiki fan here, I used to use DevonThink - which is pretty awesome, but less portable - it only runs on MacOS and has a barebones web frontend. I could carry or host my OSX VM anywhere, and use VNC or such, but TiddlyWiki is much more portable as it is a self-contained html+js file running in the browser. I loose functionality, but there's search, tagging, linking and listing and a ton of plugins. It's good enough. I used to think of the file system text file route as well, and there is this vimwiki, but as I'm used to browsing and looking up information in the browser TiddlyWiki is more convenient, and I can use SVG, mindmaps and diagrams. Emacs could be used to with the convenience of org-mode. There is also org-brain... all this is nice but is a bit more work and a bit less portable.

Regarding the potential slowing and bloating of TiddlyWiki, there is this filesystem plugin to link to local external images and documents. I use as much plain text, icons and svg diagrams as possible. I also segment several tiddlywiki's - perhaps at most 7. Now I use:

* 'VR oriented development, which is very broad and can include WebXR, UE4, Quill, C++, C#, hardware, game development, cyborg antropology, psychology

* Spirituality (meditation, christian theology, hindu tantra and buddhist philosophy) and health

* Family and friends, non-violent communication

* Tasks, notetaking, journaling, habits - including shadow work journaling (semi-spiritual/psychological practice). Work or private related, there is no seperation.

Ideally TiddlyWiki could be mounted in a FUSE-like filesystem manner, more intuitive search operators or had built-in compression to make it even more speedy but it's good enough, just like my tweaked dvorak. Perfect doesn't exist. I don't complain, I love it! I can use it on my phone and on my Quest as well.

If one day my browser grinds to a halt due to a 20 Mbyte TiddliWiki I'll think of a solution then. I think at most I'm at 16 tiddlers a day on average.

Yeah, Roam looks exactly what I'd love to have, and I would pay a licence fee; however, I don't want my knowledge hosted somewhere else apart from my computer a my backup.

I'm using Tiddlywiki as well, but I haven't customized it much yet.

Regarding your fear of it becoming slow, the good part is that you can manipulate the tiddlers easily, so you could import them in another system, if you need to migrate.