Page colour fill effects option missing

I am using version 16.101 of Word on MacOS 15.6.1

I want to set an image as the background of my document's pages, and have done so in the past by going to page colour<fill effects.

Now I can't see that option anywhere in desptop or online.

I can't use a watermark because I need the image to cover the whole page, not stopping at the margins. Does anyone know how to fix this?