If there are better opportunities, people move to take those opportunities. Mass retirements open up opportunities all across the job market, either at the positions those people left, or in the former positions of people who took the retirees’ positions. But it’s going to be the low-paid, dead end jobs that people ultimately leave behind for better opportunities when the labor supply contracts, and so that’s where the labor shortage will be most acute.
Do you really not understand this principle?