Hello,
I’m sorry I misunderstood your question earlier.
To answer your question, Microsoft updated the Photos app on Windows 11 mainly to focus on cloud syncing and folder organization. The tools for editing hidden file information, such as metadata, were removed. So you can no longer add Descriptions directly in the Photos app. So,
I would recommend trying the alternative method (the second method) suggested by Bulldog, which allows you to edit the description directly through File Explorer.