Thanks! I will have to disagree here.
Point one: While the exhaust air from the AIO will be warm, the delta will not be significantly enough above ambient temperature to cause a problematic temperature increase for the RTX 3090 Founders Edition. The Founders Edition has a heatsink and fan cooling system that outperforms most any AIB design that can easily cope with this.
Point two: While there is somewhat warm air exhausting from the AIO, there is also fresh cool air entering from the front via the 140-mm fan that will also be directly cooling the RTX 3090.
Point three: Even at full tilt, given the larger size of the fans on the RTX 3090 Founders Edition, the noise level is quite tame even at maximum fan speed. I can definitely say from experience already that EVGA's RTX 3080 XC3 Ultra is significantly louder given its smaller fans when installed in my Ncase M1.