Use querybuilder to find all pages tagged with specific tags. For eg: to find all pages tagged with "we-retail:apparel/pants"
path=/content/we-retail
type=cq:Page
property=jcr:content/@cq:tags
property.value=we-retail:apparel/pants
p.limit=-1
Refer https://sourcedcode.com/blog/aem/find-all-aem-pages-with-tags-with-query-builder
You need to write custom sling model exporter to return response in xml format. You can use javax.xml.bind.JAXBElement
Refer https://github.com/aemgeeks1212/aemgeeks/blob/master/core/src/main/java/com/aem/geeks/core/models/im...
https://github.com/aemgeeks1212/aemgeeks/blob/master/core/src/main/java/com/aem/geeks/core/exporter/... and customize as per your requirement.
https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/adobe-cq-export-content-as...
Or you can write servlet and return response to xml format.
