What is the test for finding harmlessness beyond a reasonable doubt in a case where there was no jury trial?

That is why, as we have recently observed, Neder sets "a high bar for finding harmlessness beyond a reasonable doubt" with regard to an issue never decided at all by a jury. United States v. Perez , 962 F.3d 420, 442 (9th Cir. 2020). In that circumstance, the question is not whether there is, beyond a reasonable doubt, strong evidence to support the trial judge's finding on the element in question, but whether there is sufficient evidence to support the defendant's contentions to the contrary. Id. Where there is, an appellate court cannot with any confidence predict beyond a reasonable doubt that a non-existent jury would have rejected the sufficient evidence in favor of the prosecution's case.