Explanation
Graphical user interface, text, application, email Description automatically generated

Box 1: Key Lookup
The Key Lookup cost is 99% so that is the performance bottleneck.
Box 2: nonclustered index
The key lookup on the clustered index is used because the nonclustered index does not include the required columns to resolve the query. If you add the required columns to the nonclustered index, the key lookup will not be required.