@Aurelian Negrea Xojo defines “machine” as “installation”. If you have 2 users on the same machine and you want to compile on both, then you need 2 lite license, use Desktop license (with 2 activations) or use 2 of the 3 PRO activations.
If you go to the Xojo Store page and you hover over Pro Plus 2x Activations it says “Install your license on up to 6 devices”. Again not perfectly clear.
For me, where English is not my first language, it makes sense to think as “I can install 1 license per Xojo installation”. If I only have a Mac with VM for Windows and Linux and I want to work and build on each one, I will need 3 licenses (or activations). Either 3 lite licenses or 1 Pro license that allows 3 activations. I think of this as 1 device but 3 Xojo installations (on Mac, Windows VM and Linux VM).
You only need a license if you need to build from the Xojo installation that you are working on. I have several computers and VM, in most, I only use the remote debugger. I have 2 users on my main Mac both with 1 activation and a Windows laptop with the 3rd activation. If for some reason I need to build on another computer, I need to go to my Xojo online account, remove one of the activations and assign it to the other computer.