I don’t actually know if it should unlock after completing the weekly challenge, but if so, it does not - at least for me.
Edit: I am on XSX
Edit 2: Reset cache (via software & hardware) did not help
Edit 3: reinstall and unlocking another achievement doesn’t work either
Did you complete the ultimate challenge as well?
It did unlock for me XSX as well.
Yes sir, “Hello World” is completed.
I guess it’s bugged then.
Completing the ultimate challenge gave me the achievement, have you completed that yet?
Yep completed “Hello world” but sadly no achievement.
Might be bugged them, you might want to contact Halo Support, sorry about your situation, I hate when an achievement bugs on me so I feel your pain ಥ_ಥ
Tried quitting the game (on Xbox and not resuming) fully? Or restarting the Xbox?
Sometimes with achievements you need to go to the official club for the game, look at achievements in there, look at details and it forces it to unlock it.
Xbox Guide, menu button on game, Game card, Official Club, progress, select an achievement, select launch game.
Then check your achievements again, might not have got the notification but it may now show as unlocked.
It unlocked for me on XSX, 7 hours ago.
Thanks for the reply. The club workaround did not work for me.
I mean it’s ok for me now. Not that big of a deal. Would have been nice to have the achievement in the first week, but never mind.
I had some achievements that popped up later due to some synch problem in other games. Maybe it’s kind of that.
Especially these involved kind of achievements.
Tried unlocking another achievement? In case that dislodges it?
Have you looked up the challenges page on the HaloWaypoint website and/or the smartphone app? Viewing it there might also help to dislodge it.
Also humorous to see it say “21/15 Total Challenges Completed” but the 14th (out of 15) bar of the progress indicator is highlighted 
You definitely quit and restarted the game, not ‘Resumed’ it right?
I quit it completely.
I reset the console cache.
I uninstalled the game and reinstalled it. Also it’s safe games.
I try the app hint and try to unlock another one. But I am afraid I have not enough time for this.
The rumors are right. 21/15 and the last one is highlighted. But I have equipped the visor already. So it is unlocked.