You just described my situation perfectly. My car no longer handles corners safely.
I have a 2023 MYP and just had the rear tires replaced with the exact same OEM Michelin Sport 4S 275/35/21s after 22K miles. My car performed tightly and with precision prior to the tire change. Afterwards, I now get the oscillation on long freeway stretches in autopilot at speeds over 65, and a dangerous lateral movement in the rear when entering into curves while braking, or making sudden slight movements like dodging a pothole. The rear of the car has a delayed reaction to movement which then throws the entire momentum of the car in the wrong direction at speed. It’s dangerous.
I read elsewhere that this is not an alignment problem, but instead one with the cars understanding of the old tread south versus new, and that going into service settings to recalibrate the wheels may fix it. I’m on a business trip right now so can’t do anything about it. But thought in the meantime someone might have additional insight here.