How to use the framebuffer as primary video device instead of the nvidia passed-through graphic card in a bhyve/linux vm

Hello to everyone.

what Im trying to do is to set the framebuffer video adapter as primary
graphic card on my bhyve-ubuntu vm instead of the nvidia RTX 2080 ti card
that I have passed through. What I want to do really is to use both the
graphic adapters,but the primary should be the framebuffer and the
secondary the nvidia. I tried different Xorg configurations,but what I've
got is that Xorg failed to display some errors. So,the controller that you
see below should be used as primary inside the ubuntu vm :

00:1d.0 VGA compatible controller: Device fb5d:40fb

while the ones you see below as secondary :

08:00.0 VGA compatible controller: NVIDIA Corporation TU102 [GeForce
RTX 2080 Ti] (rev a1)
08:00.1 Audio device: NVIDIA Corporation TU102 High Definition Audio
Controller (rev a1)
08:00.2 USB controller: NVIDIA Corporation TU102 USB 3.1 Host
Controller (rev a1)
08:00.3 Serial bus controller: NVIDIA Corporation TU102 USB Type-C
UCSI Controller (rev a1)


The script that I use to launch the vm is the following :

#!/bin/sh
setxkbmap it
vms="$(ls /dev/vmm/*)"
vncs="$(ps ax | awk '/vncviewer [0]/{print $6}')"

for vm in $vms; do
                session="${vm##*/}"
                echo "bhyve session = $session"
                echo "vnc session = $vncs"
                if ! printf '%s\n' "${vncs}" | grep "${session}"; then
                                printf 'VNC session not
found,destroying ghost vms\n'
                                bhyvectl --vm=$session --destroy
                else
                                printf 'Found VNC session %s\n'
"${session},no ghost vms found,not destroying them"
                fi
done

vmdisk1=`geom disk list | awk '/^Geom name: /{d=$NF} /^ *ident:
(2015020204055E)/ && d{print d}'`
echo "TOSHIBA External USB 3.0 1.8 TB ; $vmdisk1"

mount -t ufs /dev/$vmdisk1'p2' /mnt/$vmdisk1'p2'

bhyve -S -c sockets=1,cores=2,threads=2 -m 4G -w -H -A \
-s 0,hostbridge \
-s 2,virtio-blk,/mnt/$vmdisk1'p2'/bhyve/img/Linux/ubuntu2210.img,bootindex=1 \
-s 3,virtio-blk,/dev/$vmdisk4 \
-s 4,virtio-blk,/dev/$vmdisk2 \
-s 8:0,passthru,2/0/0 \
-s 8:1,passthru,2/0/1 \
-s 8:2,passthru,2/0/2 \
-s 8:3,passthru,2/0/3 \
-s 10,virtio-net,tap19 \
-s 11,virtio-9p,sharename=/ \
-s 29,fbuf,tcp=0.0.0.0:5919,w=1600,h=950,wait \
-s 30,xhci,tablet \
-s 31,lpc \
-l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI_CODE.fd \
vm0:19 < /dev/null & sleep 2 && vncviewer 0:19

For sure ,on /boot/loader.conf I've added :

/boot/loader.conf

pptdevs="2/0/0 2/0/1 2/0/2 2/0/3"

As I said before,I tried two xorg conf files to achieve the goal. On the
first one I tried to add only the framebuffer,like this :


Section "Files"
    ModulePath   "/usr/lib/xorg/modules"
    FontPath     "/usr/share/fonts/X11/misc"
    FontPath     "/usr/share/fonts/X11/cyrillic"
    FontPath     "/usr/share/fonts/X11/100dpi/:unscaled"
    FontPath     "/usr/share/fonts/X11/75dpi/:unscaled"
    FontPath     "/usr/share/fonts/X11/Type1"
    FontPath     "/usr/share/fonts/X11/100dpi"
    FontPath     "/usr/share/fonts/X11/75dpi"
    FontPath     "built-ins"
EndSection

Section "Module"
    Load  "vnc"
    Load  "glx"
EndSection


Section "InputDevice"
    Identifier  "Keyboard0"
    Driver      "kbd"
EndSection

Section "InputDevice"
    Identifier  "Mouse0"
    Driver      "mouse"
    Option        "Protocol" "auto"
    Option        "Device" "/dev/input/mice"
    Option        "ZAxisMapping" "4 5 6 7"

EndSection

Section "Monitor"
    Identifier   "Monitor0"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Device"
   Identifier  "Card0"
   Driver      "modesetting"
   BusID       "PCI:0:29:0"

EndSection

Section "Screen"
    Identifier "Screen0"
    Device     "Card0"
    Monitor    "Monitor0"
    SubSection "Display"
        Viewport   0 0
        Depth     1
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     4
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     8
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     15
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     16
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection


but it didn't work. This is the log file that shows the errors
reported : https://pastebin.ubuntu.com/p/Gv7wgsDR4K/
I have also removed the xorg.conf file,but it didn't work either. This
is the log file that shows the errors reported :


https://pastebin.ubuntu.com/p/wNcfQTByQm/

Can someone give me some suggestions that can help me to understand
where the mistake is,please,thanks.

-- 
Mario.