How does one go about measuring productivity in software? Because you can't have a meritocracy without an objective measure of performance. I think we all know

How does one go about measuring productivity in software? Because you can't have a meritocracy without an objective measure of performance. I think we all know by now that number of features shipped / commits / lines of code are not good measures, just the most visible. Also, I have come to learn that "10x developer", just means "OK developer with a greenfield project". Maybe I am just salty because my productivity is being impacted greatly right now because the software developed by our 10xer of 10 years past breaks every week and I have to fix it to get my job done.