You can long tap on the username of the thread you want to hide. It was not the most intuitive thing for me but I found it accidentally and maybe I can save you from the searching!
That behavior is about to change. There's already a jerboa update available that changes the thread-hiding trigger from long-tap on the comment header to regular-tap on the comment body (away from links and other tappable bits of the comment).
This update is available on f-droid now, but only came out yesterday I think. Might not be on the play store yet, but get ready for this to change on you.
Play store already had that behavior from at least the previous version, and just got the changed inbox behavior this morning. They're keeping parity between them pretty well.
Hahaha just tried to do it the way OP said and figured out the changed it lol. Then I read your comment... should have kept reading before spending 2min wondering why it wasn't working.
This update is available on f-droid now, but only came out yesterday I think. Might not be on the play store yet, but get ready for this to change on you.
Better yet, get your apps straight from the source by using Obtainium to manage app updates from GitHub. Not sure why I don't see this talked about more.
https://github.com/ImranR98/Obtainium
Tip: Long tap the vote counter area to access upvote and reply buttons to interact with comments from your inbox. The upvote from inbox is a bit laggy but works. This has helped me streamline a little bit.
This is something I've been trying to figure out how to do since moving over from reddit. Looks like Jerboa is an android app right? Alas, I have an iPhone… But I'm glad you worked something out!
Oh silly me. I just noticed in the regular browser view there is a collapse button next to the commenter's name. I was used to the reddit approach of clicking on the vertical line beside the thread.