If I were you I would check your logging.
Also, if you are out of shape your heart rate will be very high even for moderate exercise. The charge HR will overestimate calories burned.

So with your numbers: TDEE is of 2901 according to fitbit.
According to actual weight loss TDEE is 2'357.
Overestimating by 23%. That is quite a lot! I would only eat around 80% of the calories suggested by fitbit then.

I'm finding the same thing. I haven't had my Fitbit for that long (have the Charge 2) so I don't have the numbers you have.. but I've had a fitness tracker long enough to know how much I usually burn and Fitbit is about 500 calories above that.

In my case the problem is definitely the all-day HR monitor. My HR during exercise can get really high, up to the point where I should stop by normal standards because I shouldn't stay in peak HR that long. For about a year now I take beta-blockers for my migraines, and a happy side-effect is that my HR is lowered, which makes working out easier on me. I take the meds first thing in the morning but I bike to work about 20 minutes after that. The meds haven't taken full effect yet at that point so my HR is still higher, making the calories burned on that ride a lot higher than on my way back from work.

During the day my HR should be normal though, and I think it is as it's between 58-80. I still end up with 2700-3000 calories burned every day though, whereas my old UP24 would give me only about 2200-2500 on similar days. Back then I also had an Apple Watch so during workouts I'd get similar results to the Fitbit so it's just the all-day calories that differ.

Height adjustment, and manual correction to stride length, is a valid method of dealing with like a different BMR than Fitbit would calculate using Mifflin (or similar they actually use).

Like I'm logged about 8 inches taller to deal with higher LBM and BMR than is calculated.

Others might need to go lower. The normal variance of within 5% doesn't need correction, but 150-200 cal daily in my case I felt did so deficit wouldn't be too great and effect performance in workouts. Same amount going lower I think would benefit too. Sometimes merely having a good BF% estimate can give that clue.

So the HR-based calorie burns should also be auto-tagged an as Activity Record, with perhaps a guess as to what the activity was if not selected.
If you don't see those records, it shouldn't be using HR-based burn.

If you look at the daily graph per 5 min blocks (for better detail than 15 min) - during times of non-moving - is the base level the same when the weight/height has been the same, even on different days?

Perhaps things have changed, but it should be. Below exercise level estimating calories on HR is just plain inaccurate, I hope Fitbit didn't attempt to start doing that.
That's why they used to do the restingHR as average daily low - to try to estimate where exercise level may be kicking in.

Now - if you do have several Activity Records during the day, then it does think your HR is going higher enough for long enough to be a workout.
And if you've had the device for over 2 weeks and HR hasn't changed massively, it isn't going to get better and start figuring it out.
So indeed turn off HR unless really in a workout, I'd even suggest only on non-step based workouts - walking and running is fine to use step-based calorie burn. And lifting is never good estimate with HR either, so manually logged is better on Fitbit.

And your metabolism as a woman does indeed change during the month. And that means heat output, and HR going higher to deal with that is right on. So good observation that is very true.

@Gena575 : I was thinking about what you're seeing and it looks like your Fitbit is seeing an elevated heart rate and steps and translating that into calorie burn (which makes sense, since that's what it is designed to do).

One question is whether your heart rate is being accurately measured by your Fitbit. You might try doing spot checks to see if what your Fitbit is measuring is accurate (I have an app on my phone that uses the camera to read my heart rate by putting my finger over the camera) or wearing a chest strap HRM for part of the day if you have access to one.

If your Fitbit is accurately measuring your heart rate, but you just have a higher heart rate than normal, then maybe you could try changing the Max Heart Rate that Fitbit is using. I don't know if that affects when it uses heart rate data to compute calorie burn, rather than just using detected steps, but I do know that if you raise your Max Heart Rate it changes the exercise zones. For instance, using the default 220-age formula, my zones in Fitbit are: Fat Burn - 80; Cardio - 112; Peak - 136. (Yeah, I'm old.) But if I raise the Max Heart Rate by 10 BPM, they shift to 85, 119 & 145. What I don't know if that means that instead of kicking in the heart rate formula when my heart rate goes above 80 for a few minutes that it doesn't start using the formula until it gets over 85. But, you could try it. (You change the Max Heart Rate on the Personal Info page of the settings (that's on the website, I'm not sure where to find it on the mobile app).