https://cronometer.com/blog/cronometer-frequently-asked-questions/#:~:text=amount of fiber.-,Why Don't My Macro Calories Add Up%3F,is 9 kcals per gram.

Besides that I haven’t seen the scientific studies that back it up but there is also an answer from the cronometer forums where they said it’s based on Merrill and Watts work summarized in the book Energy Value of Foods: Basis and Derivation

https://forums.cronometer.com/discussion/2604/macros-and-calories-dont-add-up

Generally I still just follow the macros though. They also have a Thermic Effect of Food option but I choose to ignore that option as well.

I would checkout Cronometer. You can do a bit more for free like entering in your own macros which I think is paywalled on MFP.

Not sure about your devices but it’s synced with my scale and watch, so it captures my workouts and everytime I weigh myself.

I ended up paying for Gold and I can have up to 8 different group/meals and set macro schedules depending on the days of the week.

They do manage their one food database, so if you scan something that’s not there, you’re going to have to add it yourself and it may take awhile to be officially added.

Oh last cool thing that I didn’t know. Not all foods/macros are the same calorie wise. Some food for example may be closer to 3.5 cal or 4.2 per gram of protein for example so the calorie count may not exactly add up sometimes.