anjanesh Opalstack VPS are off-the-shelf Linux VPS built out with the tooling that drives our managed hosting infrastructure. The shell users on our VPS are regular Linux shell users that can do anything Linux shell users can do on any Linux system including installing software, just as they've been doing for the decades before VPS and containers existed. Our shared and dedicated servers work the same way.
The only restriction is that since the shell users don't have root access (sudo) the software must be installed entirely within the shell user's home directory. Most software supports this via configuration flags when running the installation commands but some does not. If you need to install something and can't seem to get it done due to sudo restrictions then feel free to email support, we might be able to find a workaround for you.