not iphone X, using XR here but which social media app?

Insta for me is particularly guilty

I tried both on Xs Max and Xr, no issues. Maybe try uninstalling and reinstalling the app?

If you charge it to 100%, then Apple will intentional hold the battery charge level indicator at 100% for 6-7 hours overnight to make you believe that it doesn't drain at all but that would be not a valid indication of what the overnight battery drain is. Typically I get about 5% drain overnight, but that's because I have a couple of over-active WhatsApp groups running in the background (some people don't believe in regular sleeping hours). I do have DND mode on when I sleep though.

And no, my phone doesn't heat up that much while browsing or watching Youtube, but I guess that also depends on how long you continuously browse or watch too.