hey, @straycatstrut - first of all, welcome aboard!
there is another option, that probably fits your needs even better:
swipe the bubble you want to reply to the right:
as the space in the long-tap-menu is very limited on android, and as reply is already accessible easily like above, the reply option there is the overflow menu. also, that way “reply” and “reply privately” stay together
but yeah, though swipe-to-reply is pretty common in all messenger apps, it should become a tips & tricks entry, will do that now - EDIT: did so