They are releasing a phone with official GrapheneOS support, but the operating system has to be reflashed by the user, and this phone will cost around $1,700.
Yes, but that's still a massive improvement. The phone will be much better than Pixels, and unlike Google, Motorola is actually capable of selling the phones worldwide.
It will be compatible but it won't come stock as they would breach their Google license (which is why you never see or never saw a pre-rooted phone sold by any official brand)