Ask HN: Is playing games cross-platform possible?

Is it currently possible to "build a means for games to be played cross-platform?" From my understanding, currently people on PC can only play people on PC, Xbox with Xbox, PlayStation with PlayStation, etc. but common sense via a simple thought experiment dictates that if the multi-platform games transfer and use the same data via the same database then the players should be able to connect with and play together, such as players' locations on a map and any data associated with the players. If a player using an Xbox kills a player using a PlayStation the data would be the same and therefore the player on PlayStation would be dead for all connected players regardless of the game platform they use. Firebase can integrate with Unity so it seems obvious that my thought experiment is possible unless of course the platforms are locked so as to only connect with players of the same platform. I suspect they are not and the game should be able to bypass a hurdle like that, again by means of using a database. I've had that thought experiment for several years, since 2006 I believe, so my only thought with that is that if it was possible it would have been done by now. I also feel Amazon Lumberyard could have functionality built-in to allow for cross-platform play as well with their deep integration to AWS, and with their integration to Twitch it seems to me that it should currently be the engine of choice if someone was starting a cross-platform game from scratch...

Does anybody have any insight toward this simple thought experiment? Are the platforms locked? Could games bypass the lock simply using a "single dataset?"

Thanks in advance for your consideration of my curiosity!!