Hello,
But the objective was reached on 4/01 otherwise I would not have obtained the badge "30-Day Goal Getter" on 31/01/2021.
Hello,
So is it normal that the daily goal can be modified later by Garmin once the date is in the past?
No, it is not normal, so perhpas you have inadvertently turned on the Auto-Goal feature. It can happen easily when you click the link next to the Daily Steps field (in Device Settings » User Settings).
Through this earned badget, I can tell with 100% of sureness that on 31/01/2021, the goal of steps on 04/01/2021 was reached and has be modified afterwards and if it's because I adapt my daily goal then I'm really scared to use it again
The badge prooves nothing If you accidentally activated the Auto-Goal, the goal changes each day, depending on the number of steps you do. It means the Auto-Goal may have been enabled already since a longer time, but since it kept low, it did not prevent you from meeting the goal, and getting the badge.
I'm sure 4 january was in green, that day I changed the automatic goal to a manual goal of 6,000 steps to have it green (the automatic goal is really discouraging when you don't run every day). Afterwards I was continusly checking the "Longest Goal Streak" in my personal record and it stops counting on 3/02/2021, blocked on 32 days, since yesterday it's counting again. I'm happy he took off in my first days