content-visibilty:auto seems to achieve “lazy loading” by CSS, i.e things don’t load until brought into viewport.
The way it is generally discussed in the articles I’ve seen seems to mostly refer to images but just maybe it is generally useful also for tiddlers? Might it even be relevant to speed up native TW?
I recall playing around with using it to speed up the sidebar lists. The gains weren’t always consistent but I found no downside other than the need to specify heights in advance. I also make use of it in some custom components like my Notation editor and specially templated instances of Streams.
Another thing I just came across that could speed up tiddlywiki (server), or at least improve the user experience : https://blurha.sh/
The idea is to associate a short string to an image, used to generate very quickly a blurred version of the image before the actual image finish to load. This prevent big white rectangle in image galleries.