I read today that 3.2 million baby boomers retired last year, many of them retiring early due to Covid. In addition, as deviledeggs said, Covid has killed many people. I don't remember the exact number but I think at least 100,000 of the deaths were of working-age adults. In addition, Covid has disabled many more so severely that they are unable to return to work. So I would say at a minimum, we're now looking at 3.5 million people who are out of the workforce.

If businesses had prioritized helping employees stay safe, they would have more employees now.