I can't open any files from a terminal window since hitting the return key just launches a new terminal window

Question

When I start a new terminal window (raspberrypi os, raspberry pi 4) it seems to launch correctly (it's the correct size, menus are ok, the text area is empty, etc).

I can then type text until I type a enter/return key. At that point a new terminal window is launched. This terminal window is empty just like the initial window was. So now I have two terminal windows on the desktop the first of which contains the text I just entered and the second of which is empty and has focus.

Thanks for any help.