Could you mention the exact model of the PCIE switch/host adapter you are using? The Aliexpress links are always a bit ambiguous. I am working with the c-payne switch https://c-payne.com/products/pcie-gen4-switch-5x-x16-microch...

The system is a $25k custom build with 8 video cards (4x RTX PRO 4000, 2x RTX 4090, 2x RTX 3090). That price was only valid for early 2026.