Using the Bundled Tracker is an good idea.
Under Variables -> Cross Domain Linking is enabled.
Question is now where to add the domain(s) which I want to use for Cross Domain Linking?
Or do I need to push a event like How do I accurately measure the same visitor across multiple domain names (cross domain linking)? FAQ - Analytics Platform - Matomo ?
Under Tags -> Custom Url -> “Optionally, specify a custom URL which should be tracked instead of the current location.” is stating “instead” and talk about 1 url only (which is not a domain).