I was hired for a position. And myself and the manager signed the offer letter

Then a few days later he sent an email saying he had to rescind the offer. Is that legal for them to do?

Hello,

If an employer rescinds an offer before your start date, you may still be entitled to severance or amounts to compensate you for having left your old job. This would likely depend on the terms of your contract.

Regards,

Lluc Cerda
Lawyer