There's always going to be some issue with this - because of a combo or resolution and content and more. One way to scale it up (again, depending on the content) is to do it very incrementally. Try Preserve Details or Bicubic Smoother - but if you want to rez up 200%, first do 110%, then 120%... etc. It does a better job with smaller increments. ALSO, you can maybe try resizing the lower rez image up, and aligning it on top of the higher rez image. Then, use a blending mode that may allow for the darker tones, and not apply the lighter tones - like... Multiply. In order to have a minimal effect on the lower layer - this would be incremental, too. One layer in maybe 10-15%, and then duplicating that layer. Unsure if that'll fix it, but that's how I'd start out trying... EDIT: I just tried it on the low rez screenshot I got on here, and it was best with Darken as the blend mode...
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