Is Biden's claim about masks accurate?

I fear that Biden's claim about the efficacy of wearing masks and the media's complacency in reporting it are both shams and and shames. Biden claimed that "The estimates by the experts are that it [mandatory mask wearing] will save over 40,000 lives in the next three months." A quick Google search reveals no support for the claim. The search does reveal that in June the IHME forecast that wearing masks would save 33,000 by October. Perhaps Biden rounded up and presumed that the mandate would make people go back in time to change their behavior retroactively. Otherwise, how would wearing masks for three months save 40,000 lives when wearing them for five months would save only 33,000?

Compounding the exaggeration is the lack of any attempt that I have seen by the media to press him on the basis for his recommendation. The media stresses the inability of Trump to "follow the science" and repeats endlessly that he makes statements "without evidence". What is the science that says wearing masks for the next three months would save 40,000 lives? What evidence did he provide to support his claim other a vague reference to "experts"? The media mocks Trump when he says, "people say". Saying "experts say" is no better.