cat /etc/pve/storage.cfg gives you the location of your pve storages.
(apt install gdu)
gdu -x /path/to/storage shows you the usage of the storage
(gdu is like ncdu, but much faster)
if you want to have proxmox on your laptop, you should have enough ram, but i see the problem.
(If only i had bought 64GB some time ago ;) )
Practically all my laptops are maxed out in RAM