Sorry for the trouble. It seems like a bug. Could you tell us which version you are using?

Thank you for your answer about the version. I am trying to reproduce the problem using 4.0.63 but have not yet been able to do so. We will post here if we find out anything , but we would appreciate it if you remember what you were doing just before and what you found out about the situations under which the problem occurred, please let us know.

Could you please provide the following information?:
・Display resolution
・Operating system
・UI scale configured in your operating system
・UI scale configured in the Spine editor

Thank you for the information. We have found the cause and fixed it in 4.1.26-beta. If you select multiple attachments and try to create skin placeholders, it seems to show a blank dialogue like the screenshot you attached.

As a workaround in 4.0, if you accidentally try to create skin placeholders with multiple attachments selected, click the OK button to close the dialogue, and then select only one attachment to create it again.

The UI scale setting of Spine was not related to this problem, but for your information, you can find it in the Settings… -> User Interface -> Interface scale: Settings - Spine User Guide: User interface