Others have heavily covered the legality portion of this but I want to point out one other key factor: any employer that tries to pull this kind of shit clearly has a significant employee retention problem, and they’re trying to fix it by trapping their employees financially rather than getting to the root of the problem.

Refuse to sign this agreement and find another job. If they let you join without signing this agreement keep applying elsewhere because you’ll almost certainly learn very quickly why they have such a bad employee retention problem