Yes, Google uses trunk based development for almost everything. Even Android is now on trunk based development (previously a branchy mess) and heavily uses sets of feature flags for promotion / demotion through quality lifecycles.

I’m not sure why TBD should have anything to do with code reviews. You aren’t able to submit to main without first uploading a change or stack of changes to code reviews, then you submit the changes after they are approved. That has absolutely nothing to do with your branching model. Just think of it as a rebase request instead of a pull request. PR was always the wrong terminology anyway.