HP 5530 printer
I click to print on two sides using my Mac but it doesn't. Never happened before.
MacBook Air
What operating system?
Are you using the HP ENVY 5530 e-All-In-One Printer series with Apple's built-in Airprint as a network device, or are you using some unknown/out-of-date HP printer driver that is in need of updating via HP's Smart application?
That said, my AirPrint configured Samsung ML-2955ND laser stopped printing duplex on Catalina, but not before or after Catalina, where the duplex worked normally.