We are tried the above scenario. It's working fine from our end.
We are created the below Incoming webhook URL, As see below URL both ids are different for Channel A and Channel B.
Also send the message to Channel A and Channel B as well.
Channel B--https://acb.webhook.office.com/webhookb2/47ed4773-9d2f-41ed-b9c1-34961194a089@36a708ef-700d-4d60-9de0-0a5f7b7xxxxx/IncomingWebhook/5a5a5503b4ef42898d28b03ce1f73709/4ebcc4d0-291b-4154-a85f-a89cd77aefa8
Video Link-https://youtu.be/QigIistmoaM
Microsoft Teams Version 1.5.00.34469 (64-bit)
Reference document-https://learn.microsoft.com/en-us/microsoftteams/platform/webhooks-and-connectors/how-to/add-incoming-webhook#create-incoming-webhooks-1