In host, run:
qemu-img resize debian-12-nocloud-amd64.qcow2 +5G
Change debian-12-nocloud-amd64.qcow2 to the real file name. +5G indicates increasing 30GB disk image. You can adjust the size as needed.
In Debian-derivative guest, run:
sudo apt update
sudo apt install parted e2fsprogs -y
sudo parted /dev/sda
In (parted), run:
print
fix
resizepart 1 100%
quit
and then run:
sudo resize2fs /dev/sda1
In Debian-derivative guest, run:
sudo apt update
sudo apt install parted e2fsprogs -y
sudo parted /dev/vda
In (parted), run:
print
fix
resizepart 1 100%
quit
and then run:
sudo resize2fs /dev/vda1