I love this question because it flips one of the previous questions to focus more on the individual. IMO the success of a Technical Product/Program Manager largely lies in the ‘What’ and the ‘How’.
What impact did they have? This individual measure of success should be tied to the business (product or platform) goals. The TPM should directly be held accountable for delivering on those goals. This is also the (relatively) easy part to measure (Eg: How many new users signed up for the app?, How much incremental revenue did the feature bring?, Did the platform ship on time?“
How did they land that impact? This is the ‘hard to measure’ part. For a TPM it is equally important to demonstrate leadership qualities such as - high EQ, deep Empathy, Conflict resolution, crisp communication, ability to influence without authority etc and overall be a kind and respectful individual. Often peer feedback has proven to be an effective means to gather these signals.