Interesting idea and it certainly makes sense to ensure working software at all times.

However it doesn’t have to be one or the other.

Sometimes a single commit (or PR if you prefer multiple commits) can update the api and all clients at the same time.

Sometimes client callers are external to the repo/company. In which case backward compatibility strategy is needed.

There is no need to abandon a concept of a single repo just because you might not use one of the main benefits all the time.