Did you manage to change your signature? If yes then you may cry tears of joy

In the method I described, once in edit, there's no field for "signature" per se, it's the "about me" field.....

edit: oops...the "about me" field does NOT update the signature line.....not sure what that line does, but I changed it to test and it doesn't work. So, now I'm back to not being able to see the menu item, and can't change the signature. bummer.

The appearance of that menu seems to depend on the width of the window. If the window is wide it appears as a series of entries along the bar as wreeven showed it. If the window is narrow it appears as a hamburger icon as DerPit shows. And if the width is intermediate it doesn't appear at all.

It doesn't seem to be in the power of anyone here to fix this, I guess it's Kunena Forum.

Wow. Indeed. If I enlarge the window I do get the entries in the bar. If I make it (much) narrower I get the menu. So it was not developer mode that made it show up, but the fact that the main window got narrower...
Yes, I expected that to be an issue of the forum software itself, not of any (changeable) settings...