hi @ashleigh deep filtering within links/link is not supported at the moment. You can filter why linked items id though.
So in your case, you should perform 2 queries: in the first query you search for websites having a specific regionCode and you get their ids. In the second query you search for homepages that contains the website ids you fechted before.
There is an open feature request for this at the moment: Deep filtering on both CMA and CDA - #6 by williamli You can upvote it too 