Does the 980px screen width rule still stand?

I work with a graphic designer, she was asked to create a full width slider images, she asked me about the screen width, I said I don't know it varies, she wanted a number to use when designing I google and most websites say that 980 is the standard width.

This is nothing new for me, 10+ years ago when I started create websites, they used to teach that the standard with is 980px.

I tell her that, we test her design, it becomes pixelated, 980px true size is barely 3/4 of the screen.

Is the 980px width rule still a thing? If not what's the defacto width that we should ask designers to use when designing for PC.

Is there another for mobile? I know we can make everything responsive but in case we need a number. Like say we have a slider with text on it that doesn't get resized nicely.