What is the key indicator for a tester?

Question

Project management

Hello everyone
Situation:
1) There is a testing department that does three things:
- checking tickets (bugs, updates, new functionality)
- preparing the release (checking build branches)
- handling complaints from technical support
2) It is necessary to set key indicators that determined the effectiveness of the work of the department as a whole, and of each employee in particular.
How to do it right? It’s kind of dumb to be tied to a numerical indicator, because then the quality of checking tickets may fall, and just a speed run on a number will go. How to be in such a situation?