I can't unwatch topicTrue story: unwatching a topi is a serious stuff: really difficult, and not consistent over multiple devices .
The only solution, a symptomatic one, is to mark all the messages as read and then hope that they don't populate again.
I don't think this has anything to do with multiple browsers, as is suggested in that thread. I'll quote myself here:
You're using the forum the wrong way

Clicking "unwatch" doesn't change what shows up under
Show new replies to your posts. For me, that's a long list of topics I've ever responded to in the past 10 years.
But you can edit your
Watchlist. That's the list that changes when you click "watch" or "unwatch".
Allow
me theymos to blow your mind:
Follow those directions, then just stop clicking "
Show new replies to your posts." and instead click "
Watchlist" from now on.
I know from experience changing this habit is going to take a few miss clicks.