Dear Teams user123jebwjw,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
Based on your description, I understand that you have a query "How to delete the post by Apps?"
After thorough research and consulting, it has been determined that there is currently no way to delete the automatically posted things by Apps in channel. We apologize if we are not able to meet your requirements; however, thank you for bringing this to our attention, we will surely raise your concerns to our Product Team and hopefully this can be considered in the future updates.
Moreover, I would like to invite community members and MVPs in the forum to share their knowledge or any third-party workaround and insight on this topic. In the meantime, you may create an entry as a feature suggestion in the Feedback Portal at Outlook · Community (microsoft.com), Other users may vote it and make it more visible to the service team so that it may be considered for future upgrades.
For other concerns, please do not hesitate to add you post in the Microsoft Community Team.
Thank you for your cooperation and understanding.