when running command rpm-ostree install kmod-nvidia xorg-x11-drv-nvidia
i only have rpm-fusion installed
This is an unfortunate but common issue that should be resolved soon. In the mean time, can you try running:
$ sudo rpm-ostree update --install kmod-nvidia xorg-x11-drv-nvidia
Edit: Apparently those packages are have just been added so I suspect that you will have to wait for the next Silverblue update for this to work.
As a workaround, you may be able to install the packages by downloading the conflicting packages directly and overriding them in the base image:
$ sudo rpm-ostree override replace ./libglvnd*.rpm
Then try again with:
$ sudo rpm-ostree install akmod-nvidia ...