Nowadays I have a RTX 3090ti, which is even longer than a 4090.

This solution isn't for everyone, but I made my pc case out of makerbeam rails, hanging the GPUs vertically, attached to the motherboard with PCIe x16 riser cables.

This photo doesn't show the riser cables but it does show how the GPU attaches to the rails: https://www.instagram.com/p/BMcSU_ig-Ij/