The attribute themeColor is now deprecated by design on the "new Teams"

Check here -> https://github.com/MicrosoftDocs/msteams-docs/issues/10062

It will be appreciated that someone can replace themeColor with activityImage.

Its something that will affect everyone in the near future.

I copied the code directly from the Microsoft Webhook example:

https://learn.microsoft.com/en-us/microsoftteams/platform/webhooks-and-connectors/how-to/connectors-using?tabs=cURL