Count exercise?

I've always estimated exercise calories carefully, then eaten them all back, all through almost a year of weight loss (50+ pounds) and 6+ years of maintaining a healthy weight since. Since my exercise is seasonal and weather dependent, that works well for me. On top of that, calorie counting doesn't stress me at all, psychologically: It just seems like a fun science fair experiment, to me.

Different tactics are going to work for different people. I think finding the right tactics - personalizing our approach to our own preferences, strengths, and challenges - is key to reaching and staying at a healthy weight, improving fitness, getting good nutrition. Different times in our lives may even need different tactics, so it's good to be observant and flexible.

If you decide not to separately eat exercise calories, IMO it would be a good idea to get your calorie estimate from a TDEE calculator like https://www.sailrabbit.com/bmr/, rather than from MFP. Without trying to explain exhaustively why, I'll just say that some details of the estimating calculations differ, because the assumptions are different.

As far as being harder in one's 40s, I'm a bit of a skeptic (as someone who lost at age 59-60 after previous decades of overweight/obesity). Recent research suggests metabolism is pretty steady for most people, from their 20s to their 60s.

https://pubmed.ncbi.nlm.nih.gov/34385400/

There is some evidence that repeat bouts of loss and regain can have an effect, make subsequent loss slightly more difficult. (Oversimplifying, our bodies tend to get good at what we train them to do by repetition, and repeats of loss/gain train our bodies to expect another famine (a.k.a. "diet"), so they get good at conserving energy. That won't totally prevent weight loss, but can make it a little more difficult. In addition, the way us moderns "diet" often results in accelerated loss of muscle mass, which correlates with a very slightly lower metabolic rate, but quite possibly also brings on materially down-regulated activity level (because moving is less easy/fun when we're not as strong/fit). Fortunately, that last is reversible, with attention and effort.)

I don't feel like I have good advice about what you should do, because we're quite different people. Various approaches can work. If what you did before to lose weight worked, that would be a logical thing to try this time, sure.

The one thing I'd suggest asking yourself is how the regain happened: A common issue is for people to adopt tactics for weight loss that they can't keep up long term, because they aren't sustainable. But weight management isn't a project with an end date, it's a lifelong endeavor for those of us (like me) inclined to overweight. That puts a premium on figuring out some sustainable habits that can continue almost on autopilot forever, to stay at a healthy weight after reaching there.

It's not that all of weight loss needs to use those sustainable habits, but figuring them out before reaching goal weight is a really good idea, IMO.

Best wishes for success!

You should account for exercise one way or another. Exercise calories aren't any different than any other calories you burn...they should be accounted for. They are a part of your total calorie requirements.

With MFP as designed you log exercise and get additional calories to consume. If you're consistent in your exercise you can also use a TDEE calculator where exercise is included in your activity level and thus accounted for upfront in your calorie targets and you can just customize your calorie goal on MFP and you would have a consistent calorie allotment each day.

One way or the other exercise calories should be accounted for.