Have you made any adjustments under the detail tab in ACR? See image below. Normally there is much more control with a DNG file than with a compressed jpeg or HEIF. Try increasing the luminance slider and perhaps the color slider. You can then hold down the Alt key while dragging the masking slider to find the best edges for sharpening.
I know that DNG have more flexibility with adjusting but when I saw my own RAW files in detail, they are much worse than HEIF files. I CANT EVEN ADJUST THEM. It's too grainy and too dark that I can't even recover shadow area. I got that shot directly from Lightroom CC directly. Im telling you that DNG files from iPhone X sucks. I'll post both RAW and HEIF later since it's better to see it in detail.