PUT can only create one resource, because according to the specification:
The PUT method requests that the state of the target resource be created or replaced with the state defined by the representation enclosed in the request message payload.
(https://www.rfc-editor.org/rfc/rfc7231#section-4.3.4)
However, it is possible for a request with a different verb (such as POST) to create multiple resources and return a 201 Created status. According to the specification:
The primary resource created by the request is identified by either a Location header field in the response or, if no Location field is received, by the effective request URI.
The 201 response payload typically describes and links to the resource(s) created.
(https://www.rfc-editor.org/rfc/rfc7231#section-6.3.2)
So it is OK to return the URIs of multiple created resources in a 201 response to, e.g., a POST request, but the Location header may only contain one URI.