Impossible to resize disk on Cloudmin

[nabab]

Host: CentOS 7
Guest: Ubuntu 20.04
Webmin version on both: 1.981
Cloudmin version: 9.5 Pro
Cloudmin OS: Debian 11

When I want to resize (enlarge) a disk on a KVM instance, although it is the only disk with a single partition, I always get the following error:
cloudmin update failed : Only the last partition on a disk image can be resized
Same if I do it at creation or after…

I have checked the fstab on the guest, and there’s only one line.

Do you know where it might come from?

Thanks

[nabab]

I realized the guest system had this line in the fstab:

/dev/vda1       /       ext4    grpquota,usrquota,data=ordered,relatime 0       2

while vda1 is a BIOS partition. I have changed vda1 to vda2, rebooted, and retried, and this time I got a different error about the cylinders (sorry I can’t find it) after a long while (the resizing time).
But once restarted it showed up the new right size that I had set.
I have been able to execute the resizing commands, and I could see my new size in fdisk.
if anyone interested in these, here they are (for resizing vda2):

sgdisk -e /dev/vda
partprobe
sgdisk -d 2 /dev/vda
sgdisk -N 2 /dev/vda
partprobe /dev/vda
resize2fs /dev/vda2