A Db2 function level enables a particular set of new Db2 capabilities and enhancements.
It includes code that supports new capabilities, defect fixes, and preventive service items.
Is Top Secret 16.0 compatible with DB2 function level 510?
Top Secret 16.0
DB2 12
The documentation of Function level 510 explains that It does not introduce any new features or capabilities, or catalog changes, in Db2 12 so you should not have any problem with Top Secret 16.0.