It is not possible to unlink platform accounts while cross-save is active. You would first need to deactivate cross-save, which would put all involved platform accounts into a 90 day cooldown period before they can be used for cross-save again. This would mean that your Xbox characters, which are currently playable across all of your platform accounts thanks to cross-save, would only be playable via Xbox for the duration of the cooldown period. Also, if you have purchased silver on any of your platform accounts in the past 90 days, that would prevent you from deactivating cross-save, until 90 days after the purchase date. You can read through the article linked below, for more information on cross-save, and the policies regarding its use: https://help.bungie.net/hc/en-us/articles/360049498031-Destiny-2-Cross-Save-Guide