As of the Open Beta, Enlisted's crossplay support is enabled yet again. Players can, however, choose whether they want to be matchmade with others on different platforms.

Is Enlisted Crossplay?

Enlisted does support cross-play for now. However, according to their forums, players can match up with others irrespective of the platform they're on, but they can't add them as friends. ... There are 12 different specialists that players get to choose from in Enlisted.

How do I add Crossplay friends to Enlisted?

Make sure you're at the Enlisted lobby screen where you can see your squad. Then, look at the bottom right corner where your username is shown. There are three little people with a plus next to them. Click any of these to open a new menu.