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Yeah, that app's a solid workaround. Just a heads-up, some third-party apps might ignore the theme, so you'll still see dark grey in a few spots. Let me know if that works.

+1 Oh, got it, you're looking for a true black, not just the dark theme. Have you checked the contrast themes in the Accessibility settings?

Yeah, You could also try a third-party app like Winaero Tweaker, which sometimes has deeper theme adjustments. Another option is keeping an eye on Insider builds, since pure black has been a popular feature request.