The latest InDesign version (20.3) creates target="_blank" attributes to every link when exported as EPUB. Doesn't matter if the link contains URL or it's a link from a text anchor. The latest EPUB Check version (5.2.1) gives an error with every link that doesn't have href attribute which means every text anchor is invalid.

For example:
<h1 id="_idParaDest-1" class="Header-1"><a id="_idTextAnchor000" target="_blank"></a>Foreword</h1>

In EPUB Check this is an error:
ERROR(RSC-005): Error while parsing file: element "a" missing required attribute "href"