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 – https://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
https://www.infallibletechie.com/2020/05/subscribe-unsubscribe-messagechannel-in.html