sudo apt-get update throws some error:
E: The repository 'http://ppa.launchpad.net/webupd8team/java/ubuntu focal Release' does not have a Release file.
Note: I have Ubuntu 20.04 x64.
The PPA you try to use doesn't support your ubuntu version.
Read this note: https://launchpad.net/~webupd8team/+archive/ubuntu/java:
... The PPA supports Ubuntu 18.10, 18.04, 16.04, 14.04 and 12.04. ...
Try to find a different way to install Java 8.
sudo apt-get update sudo apt install openjdk-8-jdk
Note: read this article to select the default Java version if you have installed multiple Java versions.