You can just look at the screenshots and see the Expansion. 😅 What's the problem? All the screenshots before this were made with the game's Expansion at 1280x720 (to match my screen).
And now, in the "correct" resolution of 1280x768 (and since there's nowhere to expand the picture vertically, it compresses it on the sides to fit my screen), hence the black bars.
*In general, I already see that this is a dead-end discussion. If you don't have any suggestions, I'll ask you to close the topic about the "correct screen".
(*for moderators, you can delete part of this "fluff," including my messages from this discussion, if you deem it necessary. Personally, I don't see any value in them.)
You can also look at the screenshots: on the first page, they are 1024x768 and not stretched. Starting from (approximately) the middle of the second page (comment #20), the picture is stretched from 1024x768 to 1280x720.
If you're not interested in why the game is compressing 1024x768 and stretching it to larger resolutions, then so be it.