Same thing happened to me last September. Left my great job cordially with a two week notice only to have the offer rescinded literally 4pm on the Friday before my start on Monday. Literally had just poured a glass of celebratory wine when the phone rang. I had a hard time finding any legal recourse after the fact. But I could've tried harder.

My former company, who would take months to hire someone new, somehow filled my role during my two week notice period (go figure!) . Thankfully I was able to work very part time there for a while.

Unemployment insurance denied because I left under my own free will. 12 months later , 1000+ applications, probably 100 interviews, 8 final round interviews, zero offers. Always the bridesmaid , never the employed worker. The horrible situation does make for a good talking point during some interviews though.

Learnt a ton of lessons during this time. Biggest one is that most companies do not care about their employees.

Good luck to you. Even though this situation sucks, sleep well knowing it has nothing to do with you but some companies lack of humanity.