There might be a conflict between the Nvidia and AMD Graphics drivers.
Found this article that shows which GPU cards are best for a 6 Display setup: https://medium.com/daniels-tech-world/graphics-cards-gpus-that-support-six-and-more-outputs-a1322cfc...
Here is another Multi-Monitor site that advertises MST hubs and AMD GPU card: https://multimonitorcomputer.com/best-6-monitor-gaming-video-cards.php
Please note that all Non-RX AMD GPU Cards are now legacy and not supported with AMD Driver updates. The last AMD driver for Legacy GPUs, depending on which GPU your purchase, is from 06/21/2021. So there are no Windows 11 drivers. The Windows 10 drivers should work in Windows 11 but if it doesn't then you are out of luck.
As mentioned some Consumer GPU cards can support 6 displays using one or two DP Ports on the GPU card using MST Technology.
Some MST Hubs can support 3 Displays.
AMD Professional GPU cards many support 6 Displays but not sure if at 4K resolutions or not.
It is best to get all the same manufacturer GPU Cards.
For instance with AMD GPU card that supports 6 Displays with MST Hubs you can use AMD Eyefinity to set up your displays.
I don't know if Eyefinity will work with Nvidia GPU cards or if Nvidia has something similar to Eyefinity .
Most likely you can use Windows Settings - Display to configure AMD/Nvidia GPU Cards in the same system.
