Note, that it was related to the permission. At least on my end on W11 Pro, after I removed the flag *Read-only* (default state for folders on Windows) for folder (after saving changes I agree on applying same rule for subfolders), and restarted the Tomcat, I don't have any warnings after upload/delete attachment sections. {code:none} \apache-tomcat-9.0.97\work\Catalina\localhost\xwiki{code} Hope it will be helpful.
However, it won't resolve printing warning in action to upload XAR from AdminImportSheet page.
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