If you want to unsend a message in Topics, you can delete the message. This is also possible with a message to which you have linked a file or image.
Go to the relevant message and click on the 3 dots. An overlay will appear to delete the message.
You can see for yourself in the Topic conversation that the message has been deleted.
The parents with whom you are in the Topic will also see that you have deleted the message, they will also see your name.
Note: Once you have deleted a message, you cannot undo it.