To install Unity for frontline.io 3D Studio usage, follow these steps:

1. Download Unity Hub direct link
   Or manually, go to https://unity3d.com/get-unity/download and select "Download Unity Hub".
2. After installing Unity Hub, visit the download archive, and download Unity 2020.3.21 and select the option to download it with Unity Hub.
   
   *Not installing with Unity Hub means you will not have a multi platform support.
3. Unity Hub should prompt with the installation of Unity. (This process may take several minutes)
4. Select the following modules to install (Natively Unity will only support Windows) while installing Unity select the following:

Android Build Support, iOS Build Support, Mac Build Support (Mono), WebGL Build Support

* If you want to add the platforms support at any stage, after the installation, open the Unity Hub, go to Installs, and in the relevant version settings, choose Add modules, then select the relevant modules and click install:

After installing Unity you can proceed by Creating a Project

Troubleshooting:

There are licensing issues
Cause: User is not logged in to the Unity Hub.