Incus supports only hotpluggable devices by default. Its because its code is structured that way and because of security. Add disk device usable for mounting ISO files in Windows installer · Issue #1688 · lxc/incus · GitHub
For this cases Incus offers things like raw.qemu to manually add these things for people that need it. But I understand this is not really solution when using Incus through Truenas.
My first thought would be if its possible to install nvme driver into Windows 7 and use that.
Or you can install virtio drivers. But its not that easy. TrueNAS 25.04-BETA.1 is Now Available! - #12 by TheJulianJES
If you like challenge I devised a way to install virtio drivers into already installed Windows so its identical as if you repacked it with distrobuilder.
I think the registry could be same for every windows version but I didnt check that.