Ubuntu guest Grub prompt

Hi,

I've installed (many tries) Ubuntu 21 as guest on FreeBSD 13

Installation runs without problem, but a boot, it drops to grub prompt. 
I know how to boot (set prefix=(hd0,gpt2)/boot/grub etc...)

But how to fix permanently ?

My config file :

loader="grub"
cpu=2
memory=2048M
network0_type="virtio-net"
network0_switch="public"
disk0_type="virtio-blk"
disk0_name="disk0.img"
uuid="9fb3f8a7-7935-11ec-ae5a-d05099c11279"
network0_mac="58:9c:fc:00:1b:ed"

Cheers,

Xavier

-- 
Xavier HUMBERT - Unix/Win/MacOSX Sysadmin/Network Engineer
https://www.amdh.fr