How can one add a bookmark / link to a piece of text?

This is possible, if use some HTML.

I don’t have any experience of Scrivener for Windows, but it does work on the macOS version of Scrivener.

You have to create an anchor at the target destination (word, sentence, paragraph, etc) and then create a link from the source location that points to the anchor.

The thread below includes a sample Scrivener project and its associated output to ePub.