So for a long time, I've wondered why I could never see any Mythic dungeons in the group finder.
I don't know why but whenever I went in to look for a team, I'd look at the bottom, "custom" section. I think it's because one of my guildies told me to look there for a world boss or something when I first hit 110.
So for the last however many months since Legion came out, I'd go in there to look for Mythics, and never find any except the "WTS 3 chests" crap.
I figured it was because EU, and because I was looking for lower level dungeons.
It wasn't until last night when a friend was sat next to me in RL, that I was shown the tab above, for dungeons. Low and behold my world was opened up, there was loads of Mythics of all sorts of level.
I am not a smart man, I was quite embarrassed but I thought I'd share this in case anyone else is in the same boat.
TL;DR: Played almost every day since Legion came out, only just realized there was a specific tab for dungeon on the custom group finder.