What is the format for importing Fitbit csv files?

Which kind of data do you want to import? You can import weight + body fat, daily activity (such as steps, Calories, etc), and Activities. Each of them has a different format. For exaample the format for importing the weight + fat% looks like this:

Body
Date,Weight,BMI,Fat
"2022-11-03","71.6","22.6","14.4"

There can be multiple lines of data. The first 2 header lines appear just once. Use a plain-text editor such as Notepad for creating the file. Do not use any rich-text editors like Word or Wordpad. And avoid Excel.

... and as for the daily activity, this one works:

Activities
Date,Calories Burned,Steps,Distance,Floors,Minutes Sedentary,Minutes Lightly Active,Minutes Fairly Active,Minutes Very Active,Activity Calories
"2024-01-20","0","15,726","12.04","0","0","0","0","0","0"

I do not have an example of a file for importing a timed activity, at hand, but if you search the forum, you'll certainly find examples too - start with the related threads listed here on the right side of this page.

Excellent, thanks, I'll give it a try