Unfortunately Bungie won't get involved, they don't forcibly unlink accounts from Bungie profiles and they don't deactivate cross-save to allow you to use the workaround.
You can try contacting Xbox to see if they'll hand it over but you're basically guaranteed to be told no by them, sorry to say but you're permanently stuck with that account linked unless the person that linked it gives you the login info for it.
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I found this Cross save cannot be cancelled for another 59 days because you recently purchased Silver on your Steam account. Will this help?
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You'll still need the Xbox account login information once that cooldown expires. The only way to deactivate cross-save is to authenticate every account included in the setup. As you don't have the Xbox login you won't be able to authenticate it.
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this is sad, thanks for the information