QCOW2

Enable NBD on the host:

sudo modprobe nbd max_part=8

Connect qcow2 image as a network block device:

sudo qemu-nbd --connect=/dev/nbd0 /path/to/image.qcow2

Find the VM's partitions:

sudo fdisk /dev/nbd0 -l

Mount the partition from the VM:

sudo mount /dev/nbd0p3 /mnt/point

To unmount:

sudo umount /mnt/point
sudo qemu-nbd --disconnect /dev/nbd0
sudo rmmod nbd

Install guestfs-tools (required for virt-resize command):

sudo dnf install -y guestfs-tools
sudo apt install -y guestfs-tools libguestfs-tools

To resize qcow2 images, you'll have to create a new qcow2 image with the size you want, then use virt-resize on the old qcow2 image to the new one.

You'll need to know the root partition within the old qcow2 image.

Create a new qcow2 image with the size you want:

qemu-img create -f qcow2 -o preallocation=metadata newdisk.qcow2 100G

Now resize the old one to the new one:

virt-resize --expand /dev/vda3 olddisk.qcow2 newdisk.qcow2

Once you boot into the new qcow2 image, you'll probably have to adjust the size of the logical volume if it has LVM:

sudo lvresize -l +100%FREE /dev/mapper/sysvg-root

Then resize the XFS root partition within the logical volume:

sudo xfs_grow /dev/mapper/sysvg-root