That's one of the arguments, yes. Source is here:

https://assets.documentcloud.org/documents/20519858/3-22-21-sidney-powell-defending-the-republic-motion-to-dismiss-dominion.pdf

The relevant section ("The statements at issue are protected and not actionable") begins on page 41 of the PDF, labeled as 37/54 on the top of the page itself and 27 on the bottom.

Determining whether a statement is protected involves a two-step inquiry: Is the statement one which can be proved true or false? And would reasonable people conclude that the statement is one of fact, in light of its phrasing, context and the circumstances surrounding its publication. Keohane, 882 P.2d at 1299. This inquiry is determined as a matter of law. Bucher v. Roberts, 595 P.2d 235, 241 (Colo. 1979) (“Whether a particular statement constitutes fact or opinion is a question of law.”). Analyzed under these factors, and even assuming, arguendo, that each of the statements alleged in the Complaint could be proved true or false, no reasonable person would conclude that the statements were truly statements of fact.