Hello OhTeeD2,
Welcome to the forum.
As my colleague Ubi-Karl stated, we have only just introduced our intention to use cross-play and cross--progression in our games, which is why we are asking players if they can link their platform accounts together. Please see this excerpt from the article on our Support site -
Beginning July 28, 2020, any first-party accounts that are currently linked to your Ubisoft account will remain linked to that Ubisoft account, and they will also be established as the reference accounts for cross-play and cross-progression functionality on your Ubisoft account. While you will still be able to UNLINK THESE ACCOUNTS, you must relink the same reference accounts that were originally tied to your Ubisoft account to continue accessing cross-play and cross-progression features.
At the moment, we have not confirmed or denied the possibility of using cross-progression in Siege, so please keep an eye out for any updates on the Forums or the Official Siege Twitter page, here -
https://twitter.com/Rainbow6Game