6.5" Screenshot Requirements

Use the simulator. That is what most developers do. Or just manually change the canvas size in Photoshop.

Just make sure the app itself is properly set up for the new device.

The 6.5" Xs Max displays almost the same thing as an iPhone X, except zoomed up by just over 10%.

So you can get the correct screenshot size for the Xs Max using any photo editor, including the Preview app that comes with macOS.

And you can get 5.5" 8 Plus screenshots by doing something similar with iPhone 8 screenshots.

Or just use take screenshots from the iOS Simulator if your app doesn't depend on any device only behaviors (camera, etc.)

I don't think is necessarily milking, it is just not giving a c**p.
My app was out of the app store for almost a year due to a bug in iOS, I want to get it back in but now the 6.5 requirement hits. It uses the media library so it doesn't run on the simulator. And as small dev, I only have an Xs and an older 6s. So now I can't get the app back in the store without out going through more hoops completely not of my making.
It is getting exhausting.
I guess I will see how well scaling works...sigh.

In your example, if you have a base screenshot, there may be macOS applications in the store that will generate all that are required, otherwise. Some will spit out icons as well.

Simulator doesn't work for AR apps so that isn't an option here to my knowledge. Exasperated that along with my other 5 devices I now need to go buy one of these JUST FOR A SCREENSHOT so I can deliver a point release. These sorts of forced decisions really create more and more barriers for indie shops.