When I open *.readthedocs.io docs my browser can not scroll.
ENV:
Chrome: Version 67.0.3396.99 (Official Build) (64-bit)
Device: Mac OS X

I fixed with delete overflow-x: hidden; property from html body.
Note: I can scroll other browsers like as Opera, Firefox, Safari but Chrome does not responding scroll event.
I believe this is a dupe of https://github.com/rtfd/readthedocs.org/issues/4066. According to that ticket:
Disabling 'Experimental Web Platform features' flag at chrome://flags/ seems to fix the issue in Chrome 66.
However also according to that ticket, this was supposed to be fixed in Chrome 67. I am using the identical browser version to you also on MacOS without issue so I think it is related to the experimental feature.
What a good catch, I鈥檒l try this solution and update my issue 馃敟
According to the underlying Chromium ticket, the issue is still present in 67.
I'm going to close this out but feel free to re-open if it is still an issue.