How to change the canvas background when cropping an image?

Question

Adobe Photoshop

Hello! I don’t know all the intricacies of Photoshop, so I can’t figure out how to find a solution. Previously, when I cropped images, when I enlarged the frame, the background of the canvas was white, but today I noticed that it is transparent. Maybe I accidentally pressed something, but I did not touch any settings.
Help me figure out how to return a white background, it's more convenient to work with.

Answer 1

if you have a layer, then there will be transparency;
if the image without layers will be, the background color is not necessarily white :)
the Layer→Flatten Image command will allow you to merge the layers