Which of the following criteria is not part of the new additions in WCAG 2.1?

The criterion "1.4.9 Images of Text" is included in WCAG 2.0, and it pertains to the preference for using actual text rather than images of text, except under certain conditions. This guideline aims to enhance the accessibility of text by ensuring that it can be resized and reflowed as needed, which is crucial for users with visual impairments.

In contrast, the criteria listed as additions in WCAG 2.1, such as "2.1.4 Character Key Shortcuts" and "2.1.5 Content on Hover or Focus," specifically address new challenges faced by users of assistive technologies and relate to accessibility issues that arise in modern web applications. The criteria "1.4.10 Reflow" ensures that content can be read without assistive technology on small screens by adjusting the layout accordingly.

Thus, "1.4.9 Images of Text" stands out because it is part of the original WCAG 2.0 guidelines, while the others are newly introduced in WCAG 2.1, highlighting improved focus on mobile accessibility and user interactions.