devtrackers.gg
It looks like Epic are having some authentification issues at the moment which reasonably could prevent you from being able to join online servers. Here's a link to their status page:
A temporary work around for now is to continue relaunching and closing the application, sometimes the auth does succeed and you should be able to see the button, hopefully they'll be able to resolve their issue soon.
Edit: Looks like their servers are back online as of 2 hours ago so hopefully you guys are able to see the Join button right away now :)
I think Epic runs their own servers so if you got Ark through their store them going down affects you, but idk for sure I got it on steam.
This is the general idea. Players using EGS have to be authorised by their backend to connect to our/other ARK servers. It's like when Steam is down and you're not able to play certain games because you're not able to be authed, or if Xbox Live is down, etc.
Silverlining is that this one seems to be intermittent so there's a chance to get on and usually things like this can affect many titles & systems, so it's usually a priority to get investigated and resolved as soon as possible.
We've also been able to identify some new crashes caused by this so we're fixing those up right now.