The answer is "yes," Dynamex does apply retroactively on the interpretation of "suffer or permit to work"

As opinions go these days, the California Supreme Court’s opinion in Vasquez v. Jan-Pro Franchising International, Inc. (Jan. 14, 2021) is a short one, at about 16 pages of actual text. It is also a unanimous opinion. The Ninth Circuit asked the Supreme Court to answer whether the Court’s decision in Dynamex Operations West, Inc. v. Superior Court (2018) 4 Cal.5th 903 (Dynamex) applies retroactively. The California Supreme Court concluded that it was retroactive in application:

In concluding that the standard set forth in Dynamex applies retroactively — that is, to all cases not yet final as of the date our decision in Dynamex became final — we rely primarily on the fact that Dynamex addressed an issue of first impression. It did not change a settled rule on which the parties below had relied. No decision of this court prior to Dynamex had determined how the “suffer or permit to work” definition in California’s wage orders should be applied in distinguishing employees from independent contractors. Particularly because we had not previously issued a definitive ruling on the issue addressed in Dynamex, we see no reason to depart from the general rule that judicial decisions are given retroactive effect.

Slip op., at 2. Read the decision if you want to know all about the general rule of retroactive effect and issues of first impression.