Steam based ARK servers and clients support crossplay with ARK clients running on the Epic Games Store, or EGS. While there isn't crossplay between Steam and PlayStation, Xbox, and Window Store versions of ARK, it's relatively simple to enable EGS crossplay on your server.
By default your server will only accept ARK clients running on Steam, in order for it to allow EGS (Epic Games Store) clients to connect you'll need to add the
-crossplay command line argument to the Additional Arguments startup parameter and restart your server. This was an option that was introduced in patch 311.74 and will allow EGS clients to connect to your server using the same address as Steam clients.
To disable crossplay, just remove the
-crossplay command line argument from the Additional Arguments startup parameter and restart your server.
EGS (Epic Games Store) Clients don't have access to the Steam Workshop, and by extension Steam mods. This means that running your server with any kind of mods enabled will prevent EGS Clients from connecting to the server.