Indeed, messaging someone “publicly” does not make much sense if everyone and their mother can see the message, not just the specific group of people you intended it to.
Now, how do you send a private message to several people at once? I guess I have to be “Friend” with each of them. From there is it enough to click on the username of one of them, then on the Private Message button and simply add in the Send @Username field all the other usernames?
That’s a bit convoluted. Why the Messages/Compose tabs do not offer a Private/Public message option?
I had not allowed members to upload cover photos, and that’s probably where the issue came from. Now that I did, there is a cover image space displayed (rectangular) instead of a huge avatar space (square). Pb solved, thank you.