Hi Emmanuel,
Welcome to the forum and a happy new year!
You don’t need to set a source for the posts element on archive templates. The posts element will automatically merge with the main query and fetch all related things and adapt to the context. The only thing you need to set is the template condition to archive and select for which archives you want to show your template (all archives, a specific post type, and so on).
The merge_query filter, which will be a part of Bricks 1.3.7, allows you to exclude specific posts elements getting merged with the main query. For example, if you’re using a posts element in your footer or in a sidebar that shows posts of a specific category, it can happen that it will show “No posts found”, if you’re on an archive page that does not contain posts of the specific category. Please take a look at this post from @Anushka27: How to show a category in the footer when you visit the site
I hope this helps!
Best regards,
timmse