I am unable to login to Destiny 1 on Xbox One with the error code Tapir immediately following Sign In. I do not make it to character selection and restarting my Console, Modem and re-downloading the game have no effect on the error.
This error seems to have started since I linked my Stadia account with Cross Save.
This may be because of destiny servers being under maintenance, in which case you should just wait for a couple of hours and then try again. However, if the issue remains, you may want to try unlinking your stadia account and see if it makes a difference. If that is what is causing it then it is an issue on bungies part and there isnt really much you can do about it.