First of all, looking at the other answer, AsyncAPI is not a library.
CloudEvents is a specification for describing your event data
AsyncAPI is a specification for defining API of your application that is part of event architecture. In simple words, it is like OpenAPI for REST
They both can coexist https://www.asyncapi.com/blog/asyncapi-cloud-events/
Avro is a binary data format for serialization and deserialization, like JSON or XML.
All of those can work together, your Avro can be encapsulated in CloudEvents enveloped and a number of them can be listed in AsyncAPI file that describes your application.