The issue with hover is that you have to then repeat this element on mobile and hide the desktop version on mobile (since there's no hover). And vertical may not work because you could have a note that is one line, leaving little to no space for vertical reactions. Besides, vertical is not an accustomed pattern in social networking usage. You typically want to re-use known patterns so the user doesn't need to relearn anything.
Discussion
That's a fair point - how about hover option only for desktop? Perhaps have a "..." button on mobile top right corner allowing more actions after that.
Of course if you are showing zaps, reposts etc. those need to be shown somewhere, hopefully not wasting vertical space...
I feel there is a solution somewhere, but your point is valid and i even appreciate the quick reply!!
You’ll probably have people complaining that they can’t find reactions. Also may get annoying in practice to have to hover and aim every time.
I think you’d be much better off just introducing UI scale and shrinking everything on preference