Does Cadence support Fitbit for heart rate?
The Fitbit Charge 6 supports broadcasting heart rate over Bluetooth, see details on Fitbit’s website.
Unfortunately previous Fitbit devices don’t broadcast heart rate data over Bluetooth, so there’s no way for third party apps to connect to them.
Some watch style heart rate monitors that do work are Apple Watch, Xiaomi Mi Smart Band, Garmin Forerunner 245 and 945, Whoop 4.0, etc. You can view more compatible sensors at “What Bluetooth sensors do you recommend?“