You can play Crusader Kings 3 on Steam, or you can also choose to play it from the Xbox Game Pass PC. Those who want use the PC version of the Xbox Game Pass do need to have a subscription to it, which is an excellent option for anyone who wants to give it a try before committing to purchase it. However, if you have friends who play it on Steam, can you play with them?
Unfortunately, it appears you cannot play with your friends from across the two platforms. Regardless if you make sure if the Steam user has all of their mods turned off, and you share the server name, password, and server ID, it does not work. You won’t be able to connect the two games together. It will continue to come up as not being able to connect to the server, and you don’t have the same Checksum.
Paradox Interactive may release an update in the future where the two platforms have access to one another, but following the launch of the game, this is not the case. It may change over the years of Crusader Kings 3’s lifetime.