The xbox account that's linked with my bungie.net account for crossplay is super old. Like, 15-20 years old. I cannot get it unlinked so I can use a new xbox account that I have gamepass on.
I tried updating the old xbox account with MS by accepting new ToS, assigning an email address to it, updating the p/w, but I cannot get it to unlink to Bungie when I do the "de-authenticate" steps on the bungie site.
You currently have cross save enabled on this profile. You cannot unlink accounts while cross save is enabled. If you need to replace the XBox Avocobster account you will first have to disable cross save. Once disabled you will be able to unlink the account and then link a replacement account.
Keep in mind, if you do disable your cross save you will have to wait 90 days before you can re-enable it. But if you absolutely must remove the existing XBox account then disabling cross save is your only option.