I've had a Core P3 for a while and have been pretty unhappy with the GPU riser situation.  The included 8-slot bracket causes you to either have a modern (ginormous) GPU right against the case glass where it can't breathe, or further back with the rest of the sheet metal awkwardly sticking out.  Thermaltake's GPU riser cables are also notoriously prone to failure.  This bracket holds the GPU at a nice distance but still with enough clearance for a radiator + fans on the right.  This accommodates mounting for a Okinos riser cable (link below) and also includes a support bracket for a 3090 that attaches to the top of radiator fans. Use M3 threaded inserts for I/O shield holes and M6 for mounting the riser cable/PCIe slot board.

PCIe Riser:
https://www.amazon.com/dp/B0CNNJHK93