4090 is a chunky card, so it's not going to fit in all cases, especially if PCS intends to front mount an AIO, which would reduce the max length available for a GPU. What cases and components have you tried?
I think some of the cases like the Corsair 4000 only take 240 or 280 rads on top, so if you select a 360 cooler like the H150, the configurator assumes it will be front mounted. That reduces the available GPU length. And it's surprising the number of cases that can't take 360 on top. I guess options are to see if you can select a 280 AIO instead, or source a case elsewhere and send it it. The Corsair 5000 would be able to manage the 4090 and 360 AIO I'm sure.
Spoke to PCS on phone, and apparently there are a bunch of cases not currently listed on the configurator due to being out of stock. Advised to try again over Christmas or after 5th Jan