I am already using Ubuntu desktop 18.04 Lts, do I have to install ubuntu server in Virtual Machine too for Bolt Python Library?
No. You don’t need to install Ubuntu again in a virtual machine if you already have one installed.
It is just for those who don’t have Ubuntu installed in their desktop. They can either use DigitalOcean, or a virtual machine.
No, You don’t need to install a virtual machine for installing ubuntu OS in your PC/Laptop. These projects use the Ubuntu OS or DigitalOcean for running simply into your system without any error. And you are already having ubuntu OS in your PC/laptop that’s the advantage to you for completing these projects. All the best