I was looking for pre-orders to open expecting there will be an Nvidia GPU option too (for gaming + stable diffusion image generation etc).

This has AMD Processor with integrated graphics only. I have never used a computer with AMD processors, will it be able to use Nvidia GPU later at all?

It has a dedicated AMD GPU option. That should work quite well for gaming. For CUDA ML stuff, it won't, as you suspect. (Will an Nvidia GPU come later, theoretically it could, but Nvidia is probably less willing to work with Framework ...)

Does it mean a thirdparty nvidia vendor like MSI etc can make one for framework though?