I'm not able to find the meta user option on my profile:
I have to type math.meta.stackexchange.com on Google to visit this site.
As @ArcticChar notes in the comments, it's under the profile button/dropdown:
This is a recent change: We’ve shipped some changes to the user profile navigation and this feature isn't even properly mentioned, but the responsible developer commented about it here:
Oooh, sorry it's not in the demo @Glorfindel. It shows you your Teams profiles, network profile, and meta / main site links. If there's just the one link, I plan on showing just that link with no dropdown.
All users have a network profile, so it's almost always a dropdown (it is possible to have a main site account without a meta account).