https://wccftech.com/rainbow-six-siege-crossplay-cross-progression-operation-north-star-launch-date/

Crossplay has increasingly become a standard-issue feature for multiplayer games, but Ubisoft’s Rainbow Six Siege has thus far been a holdout. Well, that will finally change over the coming months, as today during the Ubisoft Forward E3 showcase, Ubisoft Montreal announced crossplay and cross-progression is coming to Rainbow Six Siege, although there's a big caveat. Basically, folks on PC and cloud platforms (Stadia, Luna) will be able to play with each other, as well as those on Xbox and PlayStation, but PC and console players will still be kept in separate rooms. Thankfully, cross-progression will be available across all platforms.

PC/cloud crossplay will be available when Siege launches on Stadia on June 30, while Xbox/PlayStation crossplay will arrive in early 2022.