The first question is, perhaps, whether the solution, at least in the case of a table, is to widen the post. Even if it were possible, I’m not sure this would look any good.
In my eyes, the issue here (both on desktop and mobile) seems to be that the scrollability of the table is not always evident to the user. And changing that shouldn’t be too difficult (though I don’t have a solution).
Scroll bars would definitely be ugly but perhaps there are other ways of hinting at the hidden part of the table?