I would like to expand my capacity for my Home Assistant VM (vmdk). I have tried stopping the vm - clicking the name and then trying to change the capacity. No matter what I type it never sticks and just refreshes back to the original size. I have also tried putting the machine in safe mode and still the same.

Any thought on how to fix this?

vmdk needs to be converted; I suggest to convert your vmdk image to raw img, then you could use qemu-img utility to do what you want.