Share VNC temporarily

2. Is there a way to create another username/password and share just this VM (using the link) with another party?

If I understand that correctly you want to share a Screen / a Desktop and not a VM in the PVE sense. As far as I know there is no such a mechanism established yet. (I would be glad if someone proofs me wrong!)

That's why I would just use a "classic" tool like RustDesk to give adhoc access to a third party. Actually I use Guacamole as a more generic gateway to reach some machines, but that's not... really easy to setup. In my case RustDesk was and Guacamole is self-hosted, so no third-country servers involved.
 
Yea, but there are folks out there who seem to only know how to use a web browser, it's a pain to educate them on what rustdesk/etc are