I will confess I never explored Preferences thoroughly after we switched boards. My bad. Good stuff there. It’s taking some tinkering to see what effect the different choices are having on my view. But this has been immensely helpful! I’ll be sending you a big ol’ pan of ThelmaLou’s cashew fudge forthwith (as they say on Blue Bloods).
They look scrumptious. And here on the Dope they come with instant delivery, they’re diabetically orthodox, and no calories. Perfect! Thank you! 
All true! 
ETA: Before you take that next bite…clarification, please. Does “Unread” refer to replies to MY threads that I have not read? I always assumed it just meant any threads or posts that I’ve never clicked in to, which would be a lot. But under my new setup, I went to Unread and the number is 4,500+ and all the threads (i.e., “topics”) listed are ones I started. Is that the number of replies to my threads that I have not read from all time?
If this is the case, then “Unread” turns out to be a whole lot more useful than I thought it was.
“Unread” are threads where the last post Discourse knows you’ve seen is not the current last post in the thread and where the thread status is tracking or watching. So it could be a thread you’d created, or one you’ve just read or posted to.
The usual settings for notification are that threads you create are automatically set to [watching] status and (maybe) threads you read or post in are set to [tracking]. But that also depends on what your settings where when you created any of those threads or posts.
I got all my preferences set up right away when Discourse hit. So I never had any mongo backlog of threads like that. Each day now for me it’s just the ones somebody has added to since my last look at that thread.
Sorry not to be more helpful, but without knowing what your settings were the last few years and not knowing what they are now, and not seeing your screen I’m at a bit of a loss to provide more detailed “click this, then that” help.
There is a way to dismiss all unread threads. Which basically tells Discourse: “Pretend I just read every one of them up to today/now. I’m fully caught up to this very minute. But don’t change their status so I’ll still be notified afresh when somebody posts something new in any of them any time after right now.”
I don’t know recall if I’ve ever had to do that while getting my stuff set up way back when. But if I need to leave the Dope for a week or two I often use that mode when I get back. If I’m 200 posts behind in a busy thread I’ll never catch up, nor do I care that much about exactly what was said by who 10 days ago. This is a hobby, not a job.
So I push the [dismiss] button and start fresh from right now. But Discourse still knows I’m monitoring all the thousands of threads I’ve ever read. The vast, vast majority of which are simply dormant zombies never to be resurrected. And if one is, whether from 10 years ago or 2 days ago, it’ll appear in my [unread] page the next time I refresh it.
Starting to make sense?
Yes, thanks. This is very helpful.
My bold.
When I click on Unread, the number next to the word “Unread” is 4,944. Under that is a list of topics/threads I’ve started and a blue circle with the number of unread posts in that thread. In every thread, I’m the OP. Here’s a screen shot of the top of the window/page. I scroll down and down and they’re only threads where I’m the OP. I haven’t made it to the bottom of the window yet…
What you say above is what I thought Unread meant. But it seems to mean Unread in one’s own topics/thread. Unless that is controlled by a setting that I overlooked. Most of this is of not much consequence. I just like to understand stuff.
I had no idea I have been so wordy, verbose, prolific active. I guess it adds up.
That would suggest that you did not have Discourse configured to watch threads you had read or posted to. Only those you had started.
The settings you’re looking for are at your user profile page → Preferences → +Tracking. Under there the top three settings are the ones you want to / pay attention to / adjust.
The first item controls what “new” means. I use “haven’t viewed yet” which I think is the default. As you can see there are several other possibilities.
Next is what happens when you read a thread. I think the default is “never”. Which means you don’t automatically follow threads you’ve read; you’d have to explicitly switch the thread to tracking or watching manually. That’s probably what happened in your case.
I have mine set to “4 minutes”. Which means that if I skim the OP and the first couple posts and am bored, then click away or close the tab, the thread is effectively ignored forevermore unless somebody @'s me. I can see it in “Latest” when someone else posts if I go look there, but it’ll never appear in my unread.
OTOH, if I spend any meaningful time reading it, that’s evidence to me that I care about it, so after 4 minutes of that the thread automatically goes to tracking status and therefore becomes part of my unread queue. At least until I catch up to the bottom. But it’s till tracked and will once again become unread if anyone else posts to it.
The third choice is what happens if you post to a thread. I also have that set to “tracking”. So even if I don’t read the full four minutes the first time, me posting to the thread suggests to me that I’m interested in it, so I want Discourse to track it for me.
Do NOT forget to scroll all the way to the bottom and click [Save Changes] if you make changes. That is very, very easy to forget. with confusing results. Why isn’t this damned thing working??? I know I set that setting. 
Those are the settings you want to get correct for your personal approach to Dope-reading before we try to clean up the backlog of misconfigured threads from before.
Sigh. Thanks. Another pan of fudge on the way.
(Discourse wants me to PM you instead of continuing to reply to you in this thread. But I believe these exchanges may be informative to others. If not, they don’t have to read them.)
You can also set any individual thread however you want it. Look down at the bottom of the thread; there should be a little box saying normal, or tracking, or watching, and a down arrow to the right of the box. Click on the arrow, and choose your option.
Discourse is annoying about that. It seems to think it’s protecting others’ right to speak up – but this is a message board, not a conversation in person, and one person posting doesn’t prevent anyone else from doing so. I always just tell it to shut up when it does that.
I made the changes you suggested in 1-2-3.
Not sure where in Preferences this happens.
I did select and dismiss all 4,000+ plus Unread topics, so we’ll see what happens.
Off to have a pedicure now. That should clear my head!
My item 2 is the one that does that. Did you notice what it was set to before you updated it?
This is how I have it set now.
Before, I had it set to “Consider topics new when” … “created since I was here last.”
I don’t see where this would cause “only those [threads] you had started” to pop up. To me the setting would pop up what it says, namely, topics created since I last visited the board. The board automatically sets a topic to “watching” when you post in it until you change it in a thread individually. What am I not understanding?
In any case, with this new setting, and after clearing the 4,000+ unreads, now I only have three unread threads and none of them is one I created.