The in-game chat does not currently support cross play. This feature is planned to be released some time soon, but no specific date given. If you wish to voice chat now your group will need to use alternative methods until the in-game chat feature is released for cross play. I play with one friend on Playstation, me on Stadia, and one on XBox. We all three have PSN accounts. On the Playstation mobile app you can join PSN voice chats, so me and the XBox player simply join voice chat using our mobile phones and the PSN player joins the chat directly on their Playstation. The XBox app works the same. Alternatively, all players could use something like Discord to chat as well.