I second Valetudo. I’m using it on a roborock S5 and installation was pretty straight forward. Even if it takes more effort to „root“ your vacuum it is definitely worth it. I also integrate my vacuum in HA over mqtt.

Pretty much also my experience. I migrated HA stand-alone on a Pi4 to a VM on ProxMox (ThinkCenter M720) a couple weeks ago. The direct backup installation did not work so I had to create a new HA and then transfer the backup file over ssh to get it to run.

One thing I’m curious about: Do you measure the idle power consumption of your NUC and does it really drop down to 6W? Because with a Hypervisor installed I would assume that it never really goes into „idle“ hence the resources are constantly bound.

Make sure you introduce your USB dongle through ProxMox to the VM on which HA ist installed. There is an USB-option in the menu for your VM where you can choose which USB device or port from the Host should be passed trough. Once that is done figure out how the USB is connected to your HA VM via the HA shell. Something like

ls /dev/tty*

should give you the path you will need to integrate it into HA (if autodiscovery doesn’t work).