As Mike already told you, this is not an VDI solution out of the box. Most users probably access their VM's via ssh, you can use Spice for example to connect to your VM as an alternative : https://pve.proxmox.com/wiki/SPICE
This way you can connect to your VM from another machine and it will feel more like you would actually sit in front of the VM (e.g. responsiveness..).
You already discovered that there is a built in way to access the VM via our web interface, but this is meant for management tasks.
- Each target VM to be remote controlled will need either RDP or e.g. VNC running, for being able to remote control the VM. For Windows-VMs RDP is integrated, Linux VMs need to have e.g. a VNC service installed.
- Accessing those VMs from the internet needs either a fixed IP address at home or a DynDNS service to be used. In both cases you would need to port forward https/443 of your internet router to the internal Guacamole broker server(vm).
Proxmox is not a "cloud service" per se, but one strong and independent developer and provider of open source software for virtualization infrastructure. What can be the base for creating almost any "cloud service" desired on top of it.