Posting this deal as the Xbox Series X is back in stock on the Microsoft website (deal post) and these gift cards can be used to purchase it. You can buy a maximum of $500 which would mean a saving of $45 off the RRP of an Xbox Series X if you use it for that purchase
Edit: 12/05 4.27pm - Xbox Series X now out of stock at Microsoft.
Edit: 12/05 7:18pm - Seems to be going in and out of stock, if its out of stock refresh every 10 minutes or so
Can these be used for ultimate game passes as well?