I'm quite new to Stack Exchange more particularly Stack Overflow. Yet with a rep of 6 I got notifications about gaining privileges for up to 20 rep.
I can't use them so there's no real harm in those notifications; the are plain wrong.
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Here is the important information from the timeline
11:54 unaccepted A ChronosMOT 02:11 accepted A ChronosMOT
You can see the post have been accepted then unaccepted.
That means that for a few hours you gained 15 reputation, which got you at 21. Then when he unaccepted, you went back to 6.
That explains why you received the notifications for having 20+ rep.
The most likely possibility is that a question-asker briefly accepted one of your answers, bringing your reputation to 21 long enough to trigger the notifications, only to unaccept the answer.
If your reputation goes above one of the privilege thresholds, you will be notified that you gained a privilege; however, if your reputation drops back down below that threshold, you lose the privilege until your reputation once again increases at or above the threshold.
Most likely, your reputation briefly went above 20 reputation.
Note that, while an accept is the likely scenario since it's one action, it is possible two people upvoted one of your posts and then reversed their votes. Any action that increases your reputation will trigger this notification if you go above the thresholds.