it's a mutex iff it's acquiring a resource exclusively.
which you don't need to do for synchronization of coroutines since you can control in which order things are scheduled and whether that's done concurrently or not.
Not if you have multiple schedulers. Case in point: asio.strand or execution::on [1].
And even with one scheduler it makes sense to explicitly mark your critical sections.
Really, at the end of the day the primary purpose of a mutex is serialization of all operations on some data. The blocking behaviour is just a way to implement it.
which you don't need to do for synchronization of coroutines since you can control in which order things are scheduled and whether that's done concurrently or not.