Hey, Exan0!
Welcome to the forums. At this time, there is no cross-platform support for this game. All games and in-game content are attached to the platform they are activated on, so it is not possible to transfer them between platforms.
For example, if you purchased a game on your PlayStation or Xbox account, we would not be able to transfer it to PC. It is also important to note that we have no control over external account activity.
This means that we cannot make changes to your PlayStation or Xbox accounts, including transferring games or content between those console accounts.
Ubisoft Connect is the new Ubisoft gaming hub which introduces a host of cross-platform features, such as full cross-progression on highly anticipated titles like Assassin’s Creed Valhalla, Immortals Fenyx Rising, and Riders Republic however at present this does not include Rainbow Six: Siege.