I would leave it alone. There is the space (three vertical PCI slots and more than enough space towards the front, even with HDD slots), but due to the almost 3-slot-high construction of the card, there would be very little space between the fans and the side panel. Thermally less than suboptimal and definitely not recommended for a card with 350 watts power consumption. I only installed my old Vega 64 in this case because it is the Liquid Cooled Edition and therefore independent of the distance to the side panel. Without water cooling, it would probably also work with such a thick card, but the temperature rise and the associated increase in volume, including the decrease in overclocking possibilities, would not be worth it to me.

Many thanks for answers, unfortunately I almost thought so^^

I agree with Sopro. The enclosure is very generously built with lots of space, and the cable harnesses are also very easy to install. I also installed the support plate (graphics card) for the graphics card. It supports the vertical load of the graphics card.

I have only installed an ASUS GeForce RTX 2070S ROG Strix A8G gaming graphics card. In terms of mass, it seems to me to be similar to the 3090 Strix OC. It definitely fit for me. I also installed a 16.5 cm high CPU venti. Everything had room. But of course I can't give a guarantee.
VG JGB