I remember in the old days, can't remember which version, it has been too long ago I was able to check the "Show background" box to underlay the current image (at the timeline cursor) in the title editor. So I could move text according to the underlay image.
If my memory serves me right, I was able to double click on a title clip in the timeline to launch the editor which means the title clip can have the background based on the timeline. That has stopped working for many versions and I had to work around that.
Today (v20.12 Win10) I really want to know how to use that check box

you have to switch to OPENGL backend to see something on background... (but this is also bugged.. and sometimes is only black)

I set it to Auto. It works, but only when I create a new title clip. When I open an existing one the background remains blank.