Arthur Daniels shows what you can learn from the indexes on Query Store tables:
It looks like internally Query Store is referred to as plan_persist. That makes sense, thinking about how the Query Store persists query plans to your database’s storage. Let’s take a look at those catalog views vs their clustered and nonclustered indexes. I’ve modified the query a bit at this point, to group together the key columns.
This lets you see how the Query Store authors expected us to use these tables. Which isn’t always how people use them…