All depends which version you have, my watch 9 and series 2 collect the world of information which I like the fitbits when I used them were very basic.
I will type up some of the categories of data fields.
Cardio fitness
Vo2
Heart rate, heart rate variability
Physical effort
Resting heart rate
Sleep
Stages of sleep and wrist temp
Water amounts
Workouts
Resting energy
Environment noise
Weight
Stair speed down and up
Steps stride distance
Walking stride
Time in daylight
Respiratory rate
Headphone audio levels
Mood
Cardio recovery
Blood glucose
Anxiety, depression risk
Running power
Walking power
State of mind and so many more.