In the US this doesn't work well outside of college internships. Most tech workers don't want to shift to a new employer with a probation period. We already live under an "at will" employment relationship so employers can let you go anytime and workers can leave anytime. To have real value to a probation period for workers, we have to guarantee its harder to fire you past the probation period.

This will strongly favor people who believe that that they cannot get a good job, because if a candidate has multiple offers, why would they choose probation vs regular job?

(Note I am saying people who "believe" they cannot get a good job. This would be people who worry a lot, people with unusual experiences that other companies avoid, and under-performers who got fired. I am sure there will be some great hires in those groups, but likely less than during regular hiring)

That's what companies already do.

Are you suggesting that any coding interviews and challenges are simply removed from the existing processes? That just means you end up with more candidates to choose from, which doesn't sound helpful at all if your goal is to end up with better hires as the comment above was suggesting.

Even with probation the cost difference between saying no at interview and firing them during their probation is enormous.