These instructions were tested on OpenBSD 6.9 (amd64) with RemoteBox 3.0, other configurations may vary.
They describe installing the RemoteBox client and assume you have root privileges to perform the install. In order to connect from RemoteBox, VirtualBox will need to be installed and configured on the server and if necessary, appropriate firewall ports will need to be opened.
RemoteBox is available in the official OpenBSD repositories which may be sufficient for your needs, although the version may differ from the latest. It can be installed as follows:
pkg_add -r remotebox freerdp2 ssvnc-viewer
You must have your system configured to install packages from the OpenBSD repositories. Ensure the dependencies are installed as follows: