PC Can't add or play with Xbox Friends

The way I fixed it was the following;

both people join the same portal server at the same time with minimal players.   Play 5 minutes or until the round finishes.

once finished, head back to the “social” tab on the main screen. Here you will be able to look at “recent players” and your friends name will be here.  From here you can add them as a friend, and they will appear when online making it easier to “squad up” with them.