Cancel Long Running Query using Cancellation Token AND SqlCommand.Cancel()
It both cancels the Task as well as cancels the query in SQL Server. I can check the status of the query in SQL Server with select * from sys.query_store_runtime_stats to verify that the query was in fact aborted. This is important as I need to make sure it's not just canceled in the app but in the database as well.

Baaaack up a few steps. Your strategy to rely on proof of query completion by looking in a secondary table seems strange to me. If your long-running query were an update, insert etc., you would want to consider

Running your query in a transaction that does not have any kind of auto-commit enabled
Only committing at the end, once you're sure that there will be no desire for cancellation
If cancellation occurs before the commit, then you can be sure that the query was cancelled with no effect on the database

But that's not required, because your long-running query is only a select. Is there a specific reason that you don't trust Cancel to do what it's designed to do? Doing the query_store_runtime_stats check manually as a part of development testing is fine, as long as you aren't baking it in programmatically.