Gotta love image search --> https://rebeccaluncan.com/polyphemus-over-nashi/

I'm actually interested in your question, too, seeing how this is an original painting the artist is selling for $2600.

Looks like the copied the image directly from shopify cdn. Go here, click on the image for the popup, then open image in new tab. It's the exact same dimensions as the background image in op's post.

https://www.antlerpdx.com/collections/rebecca-luncan/product...

As far as I can find on the web, there are no digital copies available for sale. There is the small chance the person whom created the marketplace bought the original, but not likely.