Lets not get into the legality of this and get right down to the script that will do it for you.
Note that you need to run this script EVERY time you upgrade Proxmox.
Go to your home directory and create the script, give it execution permission and edit it. You may need to install nano if you dont have it.
cd ~ touch proxmox_disable_message.sh chmod +x proxmox_disable_message.sh apt install nano nano proxmox_disable_message.sh
Save and exit by pressing Ctrl+x followed by Y and Enter.
Now you can run the script by simply typing in: