How can we check performance at an Asset Group Level?
We can use the Listing Groups attached to those Asset Groups as a proxy for general performance, by checking spends, impressions, clicks, conversions etc for all Listing Groups per Asset Group, as a whole.
How can we check asset performance in terms of revenue/cost for videos and images?
We cannot see exact data for individual asset performance. However, we can open the Performance Max campaign, go to the Asset Group in question, click on View Details - Assets, and use the report to determine which assets are performing relatively well.
Can we get creative-wise metrics/analysis for what is picked up automatically?
We can open the Performance Max campaign, go to the Asset Group in question, click on View Details - Combinations to define the best performing Headline-Description pairs (for text) and Headline-Description-Asset groups (for images).
Where can we see audience-level insights?
These are available at the campaign level on the Insights tab, under Audience Insights
Where can we see the split between New and Returning Users on Performance Max?
This can be seen on Google Analytics.