How to install Unity Game Engine in Ubuntu 20.04
In order to install Unity Hub in Ubuntu 20.04 you need to download the older Unity Hub AppImage file which unlike the newer Unity Hub .tar.gz file can also be installed in Ubuntu 20.04.
Download Unity Hub for Linux from here. Select the Save File option and press OK. The UnityHub.AppImage file will be downloaded in the Downloads directory. Every AppImage contains an app and all the files the app needs to run. For this reason the UnityHub.AppImage file can be installed in Ubuntu 20.04 despite the different system requirements (Ubuntu 16.04 or Ubuntu 18.04) of the newer Unity Hub .tar.gz file.
Once the file is downloaded, open the terminal, change directories to the ~/Downloads/ directory, make the AppImage file executable, and run the executable AppImage file.
cd ~/Downloads
chmod a+x UnityHub.AppImage
./UnityHub.AppImage
Read the Unity Terms of Service and agree to them.
The following message will be printed in the terminal after accepting the license.
License accepted
Checking for update
Generated new staging user ID: f97abfd4-1de8-a7e2-53b5-206e7050b831
Update for version 2.4.5 is not available (latest version: 2.4.5, downgrade is disallowed).
Checking for update
Found version 3.0.0-beta.6 (url: UnityHubBeta.AppImage)
Unlike version 2.4.5 UnityHub version 3.0.0 is a beta version.
If you are running Unity Hub for the first time, click Manage License in the bottom right corner and log into the Unity Hub through Google, Facebook, or Single.
Click Preferences and select the Installs option.
Add the Unity version by selecting the Add button.
Add modules to your install and click Done.
The selected Unity version and modules will install.
When the Unity version and modules install, click the Projects tab, and create a new project.
The Unity project will open, and you can start creating games using Unity immediately.
source: revised from How to Install Unity 2020.2.1f1 in Ubuntu 20.04
