New to the group!

Pretty much, that's a nonsense message. It's "if every day were like today".

Will every day be exactly like today: Same calories, same macronutrient mix (matters for TEF), same accuracy of food labels (allowed to be off by some percent - I think it's 20% - in the US), same exact daily life routine (job, chores, whatever), same exercise at same intensity . . . when all of those are logged using estimates, not measurements?

Of course not. That message is like the "Magic 8 Ball" of weight loss: Maybe a fun party game, but useless for real life guidance.

Are you making some progress toward your goal, even if slower than you'd like? For example, if your goal is weight loss, are you gradually losing weight? If so, how much weight (roughly) have you lost over 2 months? Is that loss close to the per-week loss goal you told MFP you wanted, and was that rate sensibly moderate in the first place (like 0.5% of your current weight per week, not much faster)?

If you're logging faithfully (no unlogged cheat days) and as accurately as you can, calculate your average actual weight loss per week over the 2 months. If you could sensibly lose faster, and want to, decrease your calorie goal. If you are losing faster than sensible, or it feels unsustainably difficult, increase your calorie goal. To adjust, Use the rough estimate that 500 calories a day is a pound a week. Then monitor for the next 4-6 weeks, adjust again if necessary. (If you're adult, female, not menopausal, compare bodyweight at the same relative point in at least two different menstrual cycles when calculating average loss.)

That will work. Ignore the party-game "5 weeks" message. Some people find it motivating in some way. You obviously don't.

In fact, if you find it de-motivating, don't close your diary. That works fine. You won't see the message, and the only other consequence is that it won't put a message on your timeline saying that you completed your diary and were (or weren't) under goal. (You can post a daily update manually if that's important to you.) Not closing your diary affects nothing else.

In general, if something in the process is getting you down, think about whether there's away around it. Weight management is hard enough, without that extra stress.

Best wishes!

P.S. I've been maintaining a healthy weight for 7+ years now, after losing from class 1 obese to a healthy weight. It's been many months since I closed my diary, but it consistently says I'll gain weight "if every day is like today". In real life, my real body stays at a pretty steady weight . . . almost like these were all estimates. Go figure.