Is this project still active?

Is this project still active?

Short answer: No. Not really.

However I still would like to see native TypeScript files in core and contrib modules, but there is no out-of-box tooling for that. (I started to work on the tooling, but not even close)
Lot of thing has changed in core and in the TypeScript ecosystem since I started this project,
for example typings/typings become deprecated.

I am curious if this could be updated for Drupal 10.

If you think it would be useful to update the *.d.ts files to the latest 10.x or 11.x, then may be I can find some free time for that.

Are the ported JavaScript files done using a tool or were they all done by hand? Could they be regenerated if done with a tool?

I wrote it manually.
Back then there were no such a tool that I knew of.
It took some time, but at least I got very familiar with the core's JS API :-)
I haven't checked it, but very likely nowadays there are more than one tool for this task.

There is a related project.
https://www.drupal.org/project/typings_token →