Hello

And: what do you do with the walking 'calories'? do you eat them back (yeah, mfp is designed for them to be eaten back) and if so how do you estimate the calorie burn from walking?

Have you updated your settings on Mfp recently? If you set to to “lose 2 lbs/wk” then mfp has given you a 1,000 calorie deficit for each day. That may be too aggressive for the amount that you have to lose and your actual activity level in addition to exercise. Plus mfp goes by population estimates and you may actually require more calories than mfp suggests. I’m an easy keeper but there are many people on this forum that require more calories in order to exist.
That being said, the way to lose weight is to be in a calorie deficit achieved through diet or diet and exercise. While exercise alone burns calories, it is much too easy to take in more calories than you burn. Since you are not losing, you are not in a calorie deficit. Suggest that you weigh and log all your food and drink for at least a week. Add up all the calories at the end of the period. If you have gained weight at the end of the period, then multiply the number of pounds by 3,500 and subtract that number from the total calories. If you lost weight over the time period then multiply the pounds lost by 3,500 and add to the total calories. Take the total calories plus or minus weight lost or gained number then divide this by the number of days in the period. This will give you an idea of your maintenance calories for a day. You can use the maintenance number as your base calories and subtract 250, 500 or 750 each day to lose at a rate of 0.5lb/wk, 1lb/wk or 1.75lb/wk. The longer the period of time the more accurate your numbers will be.
You don’t need to choose the fastest weight loss. Remember that we are building sustainable habits of eating within a calorie deficit or maintenance for the rest of our lives. A slower rate of loss gives more time to practice and perfect this way of living.
Wishing you success on your journey to health

That's a very low volume of walking to expect to make a significant difference to your weight - humans are very efficient at walking and it's a low calorie burner for the time invested.
(Because of that it's more important to use net calorie estimates rather than gross calorie estimates which include what you would have burned in that time period anyway.)

For weightloss the size of the numbers involved determines the significance and the numbers from your walking simply aren't big enough compared to the thousands required to lose weight.

Good for your health and wellbeing of course, which is what exercise is really for. It's eating the right amount that will drive your weight loss.