Can't Install proxmox...unable to get device

Hi. Thanks for your help.

I am installing from a bootable USB Stick into an eMMC card in a small PC
 
The Proxmox Installer does not support installing to (e)mmc cards - mostly because those cards tend to not survive the writeload PVE causes on them for an extended period of time.

(We really recommend against running PVE on a (e)mmc card)

You can always install Proxmox on top of Debian:
https://pve.proxmox.com/wiki/Install_Proxmox_VE_on_Debian_Buster