Why would you want to install an EOL software on your system? Plesk Onyx is EOL and should not be installed anymore.
If you want to install older versions for testing purposes, please see here:
Applicable to: Plesk for Linux Plesk for Windows Question How to install beta/older Plesk versions? Answer Note: In case Plesk is already installed on a server, only the current Plesk version a...
Because my previous VPS was using Plesk Onyx, and I thought it will be compatibility issue if I use Plesk Obsidian when restoring a backup made from Plesk Onyx.
Thank you so much the info.