This is the rig with the RTX 3090 on the left.

Added two fans to push cold air at the card to keep it cool, one is cooling the back plate, and the other one on the frame is pushing air at the card.

So i tried ur setup but in my pc case . Got a fan for the backplate and one on the side . Card fans were running a bit lower so 40% instead of 70 to keep the card under 50c .
Tried it with card fans at 90% .
Still stuck at 88-89 mhs .
Really don’t think my trio x as thermal issues .