How to add a background at the end of the video with the name of the video publisher

Try looking for a title you can use that has a background color that you can change.

If the title you're using fades out at the end, you can place the playhead before the moment it fades out and use the scissors to split the clip. Delete the part that fade out. If you need the duration of the title to be longer, then you can click on the Speed icon on the right and change the clip duration.