How does one make Slack threads less narrow?

O.k., for relatively new users of Slack like me, you definitely can get a wider version of a thread, but you can't expand it directly from the thread in the righthand pane (I don't think).

What you have to do is click on All Threads in the lefthand menu pane. If you had channel content in the central message area before, it will be replaced with a list of discussions that include both channels and threads. Just scroll until you find the thread you want and then you can view it in a wider format and also continue the conversation in less cramped fashion.

This is not a solution, it is at best a "work around".

In my big-ish org there are literally hundreds of threads. There no nice way to find the thread you care about in "All Threads". There needs to be a way to navigate directly from the specific thread to that thread in "All Threads" or there needs to be a way to widen the thread display.

I noticed this week, seemingly without any announcements, that the slack app now natively supports resizing the "right-hand bar" where threads are typically rendered.

So, to answer the original question, drag it.

As a workaround, if you "Mark unread" any message in a thread, it will move that thread near the top of Threads. You can then navigate to Threads to see it in a wider view.

However, once it's read and you navigate away, the thread will drop back down to its original location. You'll also be following the thread if you weren't already.

Yes, definitely using the All Threads is the solution.

You can get it in your All Threads by sending a message to the thread, but you can also get a Thread in your All Threads by following it from the vertical "..." menu on the original message or any of the thread messages. (This way you can avoid sending a distracting comment and taking up space in the thread.)

Sending a message to the thread, though, has the advantage of bringing it to the top of your All Threads, though, which makes it easier to find once you're over there.