Single word for someone who speaks confidently, potentially falsely without data, backup or despite counter evidence

How about the word ultracrepidarian.

someone who has no special knowledge of a subject but who expresses an opinion about it

"I avoid commenting on football for fear of being called an ultracrepidarian."

You can find this word in following on-line dictionaries: Merriam Webster, Cambridge, and Oxford.

You may also want to consider the word sophist.

A person who reasons with clever but false arguments.

"Some Sophists never mind taking help of ipse dixit."

Link to this word on Merriam Webster and Oxford

As in:

I can't help but question his brazen statements.

brazen Vocabulary.com

unrestrained by convention or propriety