This option only works with the incus backend in 25.10, not with the newer one form the 26 beta.
you basically have to use the shell and
sudo incus config edit name-of-your-lxc
and add these two lines
nvidia.driver.capabilities: compute,graphics,utility,video
nvidia.runtime: "true"
it should look like this:
architecture: x86_64
config:
boot.autostart: "false"
image.architecture: amd64
image.description: Debian trixie amd64 (20251007_05:24)
image.os: Debian
image.release: trixie
image.serial: "20251007_05:24"
image.type: squashfs
image.variant: default
nvidia.driver.capabilities: compute,graphics,utility,video # <- here
nvidia.runtime: "true" #<- here
raw.idmap: |-
uid 568 568
gid 568 568
security.privileged: "false"
user.autostart: "true"
save, exit and restart your lxc and the hosts driver are now available inside the lxc
Edit: i
it was discribed in this post when incus was first introduced
and of course the incus documentation