I got banned from unlocking Minecraft achievements? What the?

You can be Banned from playing the game, but not from getting achievements.

Your achievements for that particular world or game could have gotten locked somehow. This can happen due to Mods, entering creative mode or turning on cheats. Also
your account just simply could not be synchronizing with xbox live properly, sometimes you need to allow up to 72 hours for this to happen. if the problem still persists after the allotted time and is a problem with all your worlds then I would contact the
Minecraft help center here. https://help.minecraft.net/hc/en-us or Microsoft support even if you dont think it will help you by contacting them, letting
them know that this is an issue helps things to get fixed in the future so it does not happen to someone else. It may not help you now but it could help someone later.

Delays has nothing to do with it. If it doesn't unlock for that game, then I am achievement banned from Minecraft.

I don't think you can get a achievement ban? What did you do that would make you think that you have been banned?

You cant get banned only for achievements. This kind of ban doesnt exist. There might be some other issue, better contact game support.

Have you activated creative mode on the map your playing. Once you activate creative it turns off the achievements for the world you are playing. Maybe try a new world in survival and see if they will unlock there?