Represents the metadata associated with a Lightning Message Channel. A Lightning Message Channel represents a secure channel to communicate across UI technologies (Lightning Web Components, Aura Components, and Visualforce).
To create a MessageChannel - http://www.infallibletechie.com/2020/05/how-to-create-messagechannel-in.html
The Lightning Message Service API doesn’t support the following experiences:
Salesforce Mobile app
Lightning Out
Lightning Communities
Visualforce record overrides
https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/message_channel_considerations.htm
Subscribe, Unsubscribe Lightning Message Channel in LWC, Aura and Visualforce Page in Salesforce
http://www.infallibletechie.com/2020/05/subscribe-unsubscribe-messagechannel-in.html