Hi @MasterBlaster ,
According to your description, you enabled "enforce unique value" in destination library. We are not able to use "move to" option when you set "enforce unique value" to yes in destination library. This behavior is by design.
Here is a article from Microsoft: Move or copy files in SharePoint for reference.
The Move to operation will fail if you attempt to move the document across libraries and the destination has enforced unique values.
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