Asustor Data Master (ADM) is a custom Busybox Linux, meaning a lot of things you’re used to on most regular distros aren’t the same here. You might not even know how to install stuff on it. Here’s how.
Option 1: use App Central
The App Central app on ADM’s web interface has a lot of packages. If you can find what you want there, this is your best choice.
Option 2: use the binary
For packages that provide binaries that can be readily used, you can simply move the binary to the Asustor machine and run it there.
For example, rclone offers such binary that can be easily downloaded and transferred and used.
Option 3: use opkg
opkg is a package manager originally designed for embedded Linux systems. To install it, use App Central to install Entware, and then you will have access to opkg in the command line. Then you can use it to install most things you might come across.
For example, try starting with opkg install python3 python3-pip.