I got the same problem but don’t know how to fix it. I am using MacOS 10.15.4 (iMac 27" Late 2014)
I did try to create a new scene, add canvas (UI Scale Mode: Scale With Screen Size, Reference Resolution: 1440 : 1080) and the result is just the same.
What exactly is your problem? Your screenshot shows what the background is not in front of the camera. The giant canvas box is for UI elements like Button and Image only. SpriteRenderer objects must be located inside the much smaller camera viewport box.
Set the position of your image to (0, 0, 10), then open the Game window to see how your actual game will look like.
I believe I miss understand the video, the image should be relatively similar size to the “Main Camera” and not the Canvas. so there should be no problem to fix at all