These are called post-commit code reviews, and they have been popular inside more mature teams (and at places where releases are not continuous, but done less frequently).
From The Software Engineer's Guidebook, in Chapter 23, Software Engineering:
Just learned a team at Microsoft is doing code reviews *after* merge.
Why? To move faster.
No more pausing work to wait for code reviews.
No need for stacked PRs.
No more time-consuming merge conflicts caused by long code review delays.
This has risks, but may work well for a team that is:
- mature
- high trust
- has strong automated quality checks