What is the ruling on a woman appearing fully veiled and covered in videos on "YouTube" to present useful educational content without softening her speech, or forbidden advertisements, or music, or communication with men in the comments?

The closest opinion—and Allah knows best—is that the appearance of a woman veiled, covering her entire body, has no evidence indicating its prohibition. The general principle is that anything that causes temptation is impermissible. However, a woman appearing on television immodestly or uncovered is impermissible. If she appears veiled, with her body and face covered, then there is no harm. Similarly, a woman's voice itself is not considered 'awrah (something that must be concealed), unless there is softness in speech and a yielding tone. In such a case, it becomes impermissible for her to speak in that manner to anyone other than her husband, and it is impermissible for men other than her husband to listen to it.

As for a woman addressing others with permissible knowledge, without yielding in speech or displaying adornments, she has not exceeded what is Islamically acceptable. And Allah knows best.