There is an error in the server code:

drop collection of a sharded time-series collection is not supported

… that seems to happen only when trying to drop a sharded buckets collection directly.

The error’s wording, though, makes it look like the server can’t drop sharded time-series collections at all, even via public API. That isn’t the case.

The error should instead refer specifically to the buckets. It should also guide the user to how to solve the problem. Maybe something like:

sharded time-series buckets collections cannot be dropped directly; drop the logical collection instead.