I don't have this card but according to the test tutorials you have to be careful not to bend the Adapter Cable too much. But you are right to expect the 90° adapter from cablemod. The 1200 w power supply with 4 pcie 8 pins should be good I think https://pangoly.com/en/compatibility/asus-rog-thor-1200/vga
You dont need to actually folloerd the so called ATX 3.0. ROG Thor 2 are qualified enough to run the 4090 as long you used the adapter that came along with the 4090 purchased. As mention by cekeu, as long you do not bent the adapter and your casing side panel do not cause any add on pressure against the card. yo are safe. And most important that does not violate the Asus Warranty .