Bruce,

Question: How does one find a hidden topic (or message) in order to
unhide it later?

In my concept they remain visible to mods and owners.

How are they flagged so those with the proper privileges to see it
know that other cannot (new status badge)?

Like a locked or moderated topic, I proposed an eye-slash icon (badge) to the left of the subject text.
https://beta.groups.io/g/main/message/22337

Like those other two, this would be an independent attribute that can be applied alone or in conjunction with the others.

Oh, interesting. The other two only stack up in search results. E.g.:
https://beta.groups.io/g/main/search?ev=false&q=%22Thread+view%22&ct=1
In other views locked seems to take precedence over moderated.

I would want hidden to stack next to the other icon(s) if any, it shouldn't take precedence over either, nor should either take precedence over hidden.

If a "Hide Message" function were (also) implemented there's a small question of where to put the icon when looking at a topic containing that message (as the Subject text is only shown at the top of the topic page). I think it should still be at the top, so somewhere among the Posting member identification on the left and the date & message number on the right.

Shal