I am getting a new bike (Giant Revolt Advanced 3) and because of GRX being completely out of stock I am not able to upgrade the GRX400 that comes with it. I will have to do it later. Since I have a Shimano XTR Shadow 2008 groupset in very good conditions, my idea was to mount this group but only with two chainrings. This way I can sell the GRX400 parts and not lose that much money since I do want to upgrade whenever becomes possible. 

Now, my question is if there is any way of having brifters (Sora?) working with XTR 9 speed mechs and at the same time compatible with the existing hidraulic disk brakes (GRX400)? 

If I must guess I think this may be an impossible mission but not Tom Cruise style, with some kind of workaround possible.