how to install the DDE to the ubuntu 20.04?

I have installed the Ubuntu 20.04, and want now I want to install Deepin Desktop Environment (dde)

My steps are:

• add the ppa and install using apt

  sudo add-apt-repository ppa:leaeasy/dde
  sudo apt-get update
  sudo apt install dde
  

But during the command sudo add-apt-repository ppa:leaeasy/dde I get the following error:

$ sudo add-apt-repository ppa:leaeasy/dde
 You can install deepin desktop environment by run

sudo add-apt-repository ppa:leaeasy/dde
sudo apt-get update
apt-get install dde
------
Ubuntu Bionic: https://drive.google.com/file/d/1xkQPb4tWocknuYeY-t41W--kz-9SSL0V/view?usp=sharing
------
Important Issue:
Q: Can dde on Ubuntu 16.04?
A: Sorry, the dde depends on qt version above than 5.6.
     If you want to install dde, please upgrade to 17.04 or above.
 More info: https://launchpad.net/~leaeasy/+archive/ubuntu/dde
Press [ENTER] to continue or Ctrl-c to cancel adding it.

Hit:1 http://in.archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease                                     
Hit:3 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease                                   
Ign:4 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal InRelease                                     
Hit:5 http://security.ubuntu.com/ubuntu focal-security InRelease           
Err:6 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release          
  404  Not Found [IP: 91.189.95.83 80]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

I get the similar error with sudo apt-get update :

$ sudo apt-get update
Hit:1 http://in.archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease                                      
Hit:3 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease                                    
Ign:4 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal InRelease           
Hit:5 http://security.ubuntu.com/ubuntu focal-security InRelease
Err:6 http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release
  404  Not Found [IP: 91.189.95.83 80]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/leaeasy/dde/ubuntu focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

How can I install dde ?