What is Cardinality Estimation or SQL CE Level?
The Cardinality Estimator is a SQL Server Query Processor component that is responsible for predicting the number of rows that the query will return. Microsoft provides some great documentation about SQL CE which you can read more on Microsoft Docs.

As for how SQL CE works and it’s importance with ConfigMgr, Umair Khan of Microsoft has shared a great blog post explaining the details, which you can read more here:
https://blogs.technet.microsoft.com/umairkhan/2019/01/28/configmgr-current-branch-1810-guidance-for-the-sql-ce-levels-with-various-sql-versions