Office Scripts

At the moment there is no WordScript object model.
You have to use Office Add-ins which is a superset of Office Scripts.

Add-ins

link - github.com/OfficeDev/Office-Add-in-samples/tree/main/Samples/word-add-in-load-and-write-open-xml 

Add-ins - Range.insertOoxml

var ooxmlText = "<w:p xmlns:w='http://schemas.microsoft.com/office/word/2003/wordml'>" +  
"<w:r><w:rPr><w:b/><w:b-cs/><w:color w:val='FF0000'/><w:sz w:val='28'/><w:sz-cs w:val='28'/>" +  
"</w:rPr><w:t>Hello world (this should be bold, red, size 14).</w:t></w:r></w:p>"; 
var range = context.document.getSelection(); 
range.insertOoxml(ooxmlText, Word.InsertLocation.end); 

range.insertOoxml(" XML CODE", Word.InsertLocation.start); 

<pkg:package xmlns:pkg='http://schemas.microsoft.com/office/2006/xmlPackage'>  

<pkg:part pkg:name='/_rels/.rels'  
pkg:contentType='application/vnd.openxmlformats-package.relationships+xml'  
pkg:padding='512'>  

<pkg:xmlData> 
<Relationships xmlns='http://schemas.openxmlformats.org/package/2006/relationships'>  

<Relationship 
Id='rId1'  
Type='http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument' Target='word/document.xml'/> 

</Relationships> 

</pkg:xmlData> 
</pkg:part> 

<pkg:part pkg:name='/word/document.xml'  
pkg:contentType='application/vnd.openxmlformats-officedocument.wordprocessingml.document.main+xml'>  

<pkg:xmlData> 
<w:document xmlns:w='http://schemas.openxmlformats.org/wordprocessingml/2006/main' >  
<w:body> 
<w:p><w:pPr><w:spacing w:before='360' w:after='0' w:line='480' w:lineRule='auto'/> 
<w:rPr><w:color w:val='70AD47' w:themeColor='accent6'/><w:sz w:val='28'/></w:rPr></w:pPr>  
<w:r><w:rPr><w:color w:val='70AD47' w:themeColor='accent6'/><w:sz w:val='28'/></w:rPr>  
<w:t>This text has formatting directly applied to achieve its font size, color, line spacing, and paragraph spacing.</w:t></w:r></w:p> 
</w:body> 
</w:document> 
</pkg:xmlData> 

</pkg:part> 
</pkg:package> 

Add-ins - Range.getOoxml