One thing I miss in TiddlyWiki, that is now a standard on most text-based interfaces (eg in Notion, but also in Github and Gitlab for example), is the ability to quickly make todolists by simply adding [ ] / [x] to the start of a bulleted list, e.g.
* [x] A checked item
* [ ] An unchecked item
producing an interface with a clickable checkbox that, when checked, edits the actual line and not a field somewhere else.
(both in TW5 and markdown tiddlers)
I think @well-noted will publish this in his update of the streams plugin
Yes, it is not part of core, but it exists as plugin feature. Examples are kara, table-csv shiraz
There are other plugins around.
Goto Kara 0.8.1 — In tiddler plain checklist and interstitial journaling
Open a new tiddler
Paste <<checklist>> and save
if you don’t like a UI, use <<checklist showInput:"no">>
https://cdruan.github.io/tw-markdown-more/
Here is a plug-in by @cdruan for markdown checklists
If you like something ready, then download the Mehregan Edition, a Zettlekasten based personal knowledge management (PKM) app.
Demo and code
Every tiddler has a Todo section, appears at the bottom of tiddler. You can add your todos manually or by using the provided UI. See the below screencast.
To be clear, my opinion is that Streams already has everything someone would want for an ideal todo list – the demo I’m working on will be better, I’d argue, because it would not require a Headline tiddler for the list, but I’ve already shown how to create an ideal(ish) todo list.
The one thing in streams that would make this better would be an update that makes custom viewtemplates and contextmenus easier than modifying a shadow tiddler.
These other suggestions are fantastic ways to build TODO lists if you are not a streams user 
