Bummed to report firsthand that the GRX hoods are not compatible with the 105 R7020 levers at least. The outer shape is identical, but the Trek dealer was right about the inner moldings being different to the point that it doesn't fit on the lever body correctly at all. The left is the inside of a 105 hood, the right is the GRX. Someone would have to post a similar photo of an Ultegra R8020 hood to see if it's completely different as well.
