My page title turns into a h2 tag – What to do?

You need to alter the template files under the theme folder. In the folder template-parts there is content-page.php that renders the page (well, at least the part with the header) and content-single.php that has the single post’s title part.

Just change the <h2> and </h2> tags to be <h1> and </h1> respectively on the <?php the_title( '<h2 class="entry-title">', '</h2>' ); ?> part.