What’s the current state of recommendation algorithms/systems in machine learning research? [D]

When I first started my ML journey about 4 years ago the most basic intro level recommendation algorithms I learned were about collaborative filtering and content based filtering.

I want to know more about what the current state of recommender systems is. How has it changed? What methods are people trying to include in search of better recommendations? Has there been any mention of including causality in recommendation systems? This latter seems like the most “up to date” advancement, but …

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