How do Xbox gold quests work?

So a little while back I saw a notification on my xbox home landing page for a "quest" which some "mystery prizes". This was the October 2018 quest, I completed it and quite enjoyed the promotion. I've read around this forum and apparently there have been
several more months of quests which I've just never seen anything for - no email, nothing I can find on the web, no notifications or messages on my xbox.

Based on that I was wondering how the quests work and how you can find out what they are for any given month.

other key information/thoughts:

- I am not referring to the game pass quests

- is there a region lock on the quests?

Any insights are greatly appreciated - thanks in advance!

:)