1) Resize the VM Disk in PVE

Precautions

Stop!
Take a snapshot or backup of your VM in its current state for easy rollback in the event of failure or data loss.

Extend the Disk in PVE

GUI

Example VM: Windows 11, current disk size: 75 GiB

Select Hardware menu and select the current disk

Click "Resize"

When resizing, you will not be declaring the new disk size. You are indicating how much more storage to add to the disk.

Add an additional 5 GiB of storage to the disk and click "Resize disk"

Disk resizing on PVE is now complete. You must log into the VM and expand any partitions / volumes.