TinyMCE How to change default font-size for "Clear Formatting" Button

You can use content_css or content_style to define your default settings.

If you have a css file with your defaults, you can define it in the following way:

tinymce.init({
  selector: "textarea",
  content_css: "/mydefault.css"
}); 

Just define the path to that css file with content_css. Even multiple css files can be defined comma separated.

Apart from defining a file, you can also define the style directly:

tinymce.init({
  selector: "textarea",
  content_style: 'font-size: 10px; font-family: mono'
}); 

This defines a custom font size and family.
2022-02-11 at 16:49