Adding on top: While Proxmox VE is indeed meant to run headless by default (most servers don't have much use for a desktop) you can install any Linux Desktop that's available in Debian, for example GNOME, KDE, XFCE, ... just fine.
Source: I'm writing this post through my PVE powered workstation using i3 as window-manager (a bit advanced, would not recommend it for beginners) and plain old Firefox.
See the wiki for a rough article about that:
https://pve.proxmox.com/wiki/Developer_Workstations_with_Proxmox_VE_and_X11
Or for GNOME specifically:
https://wiki.debian.org/Gnome
KDE Plasma:
https://wiki.debian.org/KDE?action=show&redirect=Plasma#Installation
The (a bit lighter compared to above ones) XFCE:
https://wiki.debian.org/Xfce