Buggy makeappx or docs?

makeappx says my manifest is incorrect after I changed it according to docs.

Docs: https://docs.microsoft.com/en-us/windows/uwp/porting/desktop-to-uwp-extensions#open

Change:

<uap:Extension Category="windows.fileTypeAssociation">
    <uap3:FileTypeAssociation Name="torrents" UseUrl="true" Parameters="%1">
      <uap:SupportedFileTypes>
        <uap:FileType>.torrent</uap:FileType>
      </uap:SupportedFileTypes> 
    </uap3:FileTypeAssociation>
</uap:Extension>

Error it generates:

MakeAppx : error: Error info: error C00CE015: App manifest validation error: The app manifest must be valid as per schema: Line 44, Column 55, Reason: The attribute 'UseUrl' on the element '{http://schemas.microsoft.com/appx/manifest/uap/windows10/3}FileTypeAssociation' is not defined in the DTD/Schema.

MakeAppx : error: Package creation failed.

MakeAppx : error: 0x80080204 - The specified package format is not valid: The package manifest is not valid.