Hi Jhifi
To upload an image from Downloads, select Upload or From this device in Designer. When the File Explorer window opens, choose Downloads from the left-hand navigation pane. If it is not shown, enter %USERPROFILE%\Downloads in the address bar and press Enter.
This confirms that Designer itself is saving the edits correctly, and the issue appears to be with the Designer integration in the Photos app. For now, uploading directly to Designer is the recommended workaround.
Thank you for your time and if you find my answer helpful - please feel free to click "Yes" - this will help the user experiencing the same issue.
Have a great day