Gist for my article Building a Gutenberg sidebar plugin Part 5: Outputting data https://vanaf1979.nl/building-a-gutenberg-sidebar-plugin-part-5-outputting-data/

metatags-morehooks.php

<?php
public function register() : void {

    ...

    \add_action(
        'after_setup_theme',
        array( $this , 'add_title_theme_support' ),
        1
    );

    \add_action(
        'pre_get_document_title',
        array( $this , 'add_title_to_head' ),
        999
    );

    \add_action(
        'wp_head',
        array( $this , 'add_metatags_to_head' ),
        1,
        1
    );

}