What is a hydrogen bond acceptor and donor?
Dissenter's answer which you linked appears to be wrong (as of now). I have left a comment.

The conventional way in which we talk about hydrogen bond acceptors/donors is: in a hydrogen bond $\ce{X-H...Y}$, the hydrogen bond donor is $\ce{X-H}$ and the hydrogen bond acceptor is $\ce{Y}$. (See for example Chem LibreTexts, or this other question on hydrogen bonds.)

Of course, water is capable of acting as both an acceptor and as a donor:



I wouldn't call it a "proton donor" like Wikipedia does, though, as that suggests some kind of acid-base reaction occurring, like

$$\ce{\color{red}{H2O} + \color{blue}{H2O} &lt;=&gt; \color{red}{OH-} + \color{blue}{H3O+}}$$

In this reaction the red water molecule is acting as a proton donor (Brønsted acid) and the blue water molecule is acting as a proton acceptor (Brønsted base). But these terms should only be used in the context of a proton transfer, and not hydrogen bonding.