Been building rigs for over a decade and honestly the Cooler Master Universal Vertical GPU Holder Kit V3 PCIe 4.0 is my top pick for heavy cards like the 4090. Im really satisfied with how it handles the weight without any sagging. The main reason it wins for airflow is the modular design. You can literally slide the GPU base back and forth on its rail. This lets you push the card much closer to the motherboard and further away from the side glass than the Lian Li Universal Vertical GPU Multi-Angle Bracket Kit VG4-4-V2X usually allows. Having that extra gap for the fans to actually pull air is vital when youre dealing with a 450W card. It works well in basically any mid-tower and the build quality is sturdy enough that i dont worry about my hardware. Definitely get the CM version if thermals are your priority.

I totally see why the CM kit is popular, but the Phanteks Vertical GPU Bracket Gen4 Black is an amazing alternative for your 4090! It's fantastic for budgets under $75. Methodically, it positions the card much further back from the side panel than the Lian Li. That extra air gap is basically essential. Love how it keeps temps low without costing a fortune... definitely worth looking into.

In my experience, the EZDIY-FAB Multi-Angle PCIe 4.0 GPU Mount wins for airflow tho. Tilting it slightly kept my 4090 from choking against the glass during long sessions.