System.Xml.Linq can be used to create a document from scratch. For example:

using assembly System.Xml.Linq 
using namespace System.Xml.Linq 
 
$xDocument = [XDocument]::new( 
    [XDeclaration]::new('1.0', 'utf-8', 'yes'), 
    [XElement]::new('list', @( 
        [XAttribute]::new('type', 'numbers'), 
        [XElement]::new('name', 1), 
        [XElement]::new('name', 2), 
        [XElement]::new('name', 3) 
    )) 
) 

Converting the xDocument object to a string shows the document without the declaration:

PS> $xDocument.ToString()
 
<list type="numbers"> 
<name>1</name> 
<name>2</name> 
<name>3</name> 
</list> 

The Save method may be used to write the document to a file:

$xDocument.Save("$pwd	est.xml") 

Reviewing the document shows the declaration:

PS> Get-Content test.xml 
<?xml version="1.0" encoding="utf-8" standalone="yes"?> 
<list type="numbers"> 
<name>1</name> 
<name>2</name> 
<name>3</name> 
</list>