Drupal 11: Strip Tags From Field In Migration

To strip the HTML tags from a field in the migration you just need to use the "callback" plugin, which is part of the core Migrate module.

  field_article_text:
    plugin: callback
    callable: strip_tags
    source: field_html_content/0/value

The field_article_text field will now contain the content from the text field field_html_content, minus any HTML tags.