Android currently shows a small key icon on the top right corner to represent that VPN is turned on, and it also shows a message on the control panel saying:
[This device is connected to the internet through <name of the VPN>. Your network activity, including emails and browsing data, is visible to the VPN provider.]
Although it won't be a high priority task, could GrapheneOS make an option to hide the key icon and that obvious message about VPN connection?