Reproduced from my comment in this discussion...

The Fabric Gateway client API (similar to the fabric-network package that preceded it) focuses only on enabling client business applications to invoke (evaluate and submit) transactions, and receive chaincode and block events. It intentionally omits capability for administrative operations, such as chaincode deployment, channel creation, or identity registration / enrolment.

For administrative tasks, there are a few potential options:

• Use the Fabric CLI commands.
• If deploying to Kubernetes, a Kubernetes operator designed for managing Fabric might provide the capability you need. Two alternatives that I know of are Hyperledger Fabric Operator and fabric-operator.
• Continue using the existing fabric-ca-client. While it is no longer actively developed, the Fabric CA is pretty stable in its capability so this client API should continue to work.
• Use the REST API of the Fabric CA directly with your own client. I don't know of any specific documentation of the API, but the fabric-ca-client implementation just interacts with the Fabric CA using HTTP requests. You could inspect the implementation (or perhaps the unit tests to identify the correct HTTP request structure. The Swagger definition of the CA REST services and this StackOverflow post might also be helpful.

For chaincode deployment and channel management, there is a pretty complete Golang implementation in the fabric-admin-sdk repository. That repository also contains a Node admin implementation (based on code developed here) with code to interact with the CA. I am not sure how stable and/or functional the Node implementation is.