If you have websites on different domains and want to manage the XML site maps centrally for all of them Google allows, and encourages this, using Cross-Domain verification.
Using cross-domain verification enables one of the most efficient methods for managing your large HREFLand XML site maps. By adding all of the domains in a master Google Search Console account Google is able to verify your ownership of all and then allows for your HREFLang XML to be uploaded in a single set of files for all domains in the portfolio.
Leveraging this feature, many of our enterprise clients or those with complex IT challenges will create a separate domain outside of your technical stack such as “mysitexml.com” and host all of the XML site maps in this location. Since this domain does not impact the main website you can allow HREFLang Builder to automatically upload to this domain. This adds significant flexibility to your overall management.