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I tried those two command and get some error:

i) sudo add-apt-repository ppa:flexiondotorg/albert

An amazing, desktop environment agnostic, omnilauncher.

https://github.com/ManuelSchneid3r/albert

 More info: https://launchpad.net/~flexiondotorg/+archive/ubuntu/albert

Press [ENTER] to continue or Ctrl-c to cancel adding it.



Ign:1 http://dl.google.com/linux/chrome/deb stable InRelease                   

Hit:2 http://dl.google.com/linux/chrome/deb stable Release                     

Hit:4 http://mirror.dhakacom.com/ubuntu-archive bionic InRelease               

Get:5 http://mirror.dhakacom.com/ubuntu-archive bionic-updates InRelease [88.7 kB]

Ign:6 http://ppa.launchpad.net/flexiondotorg/albert/ubuntu bionic InRelease    

Get:7 http://mirror.dhakacom.com/ubuntu-archive bionic-backports InRelease [74.6 kB]

Get:8 http://mirror.dhakacom.com/ubuntu-archive bionic-security InRelease [83.2 kB]

Hit:9 http://ppa.launchpad.net/noobslab/apps/ubuntu bionic InRelease           

Hit:10 http://ppa.launchpad.net/notepadqq-team/notepadqq/ubuntu bionic InRelease

Err:11 http://ppa.launchpad.net/flexiondotorg/albert/ubuntu bionic Release     

  404  Not Found [IP: 91.189.95.83 80]

Hit:12 http://archive.canonical.com/ubuntu bionic InRelease                    

Reading package lists... Done                                                  

E: The repository 'http://ppa.launchpad.net/flexiondotorg/albert/ubuntu bionic 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.

ii) sudo apt-get update && sudo apt-get install albert

Hit:1 http://mirror.dhakacom.com/ubuntu-archive bionic InRelease               

Get:2 http://mirror.dhakacom.com/ubuntu-archive bionic-updates InRelease [88.7 kB]

Get:3 http://mirror.dhakacom.com/ubuntu-archive bionic-backports InRelease [74.6 kB]

Get:4 http://mirror.dhakacom.com/ubuntu-archive bionic-security InRelease [83.2 kB]

Ign:5 http://dl.google.com/linux/chrome/deb stable InRelease                   

Hit:6 http://archive.canonical.com/ubuntu bionic InRelease                     

Hit:7 http://dl.google.com/linux/chrome/deb stable Release               

Ign:9 http://ppa.launchpad.net/flexiondotorg/albert/ubuntu bionic InRelease

Hit:10 http://ppa.launchpad.net/noobslab/apps/ubuntu bionic InRelease

Hit:11 http://ppa.launchpad.net/notepadqq-team/notepadqq/ubuntu bionic InRelease

Err:12 http://ppa.launchpad.net/flexiondotorg/albert/ubuntu bionic Release     

  404  Not Found [IP: 91.189.95.83 80]

Reading package lists... Done                                                  

E: The repository 'http://ppa.launchpad.net/flexiondotorg/albert/ubuntu bionic 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.

need help...
thanks in advance :)

Albert is my favorite quick launcher, so I have it installed in Ubuntu 18.04. The errors you are getting appear to reflect temporary or perhaps permanent problems with the PPA.

Installing through PPA

The User guide of Albert refers for more instructions to a site of openSUSE. There, you click on the Ubuntu icon. You will find instructions there to connect to a PPA that is different than the one you attempted.

Installing through a .deb installation file

I prefer to install Albert by downloading a .deb installation file. The advantage is that you do not need to add an external PPA. The drawback is that the program will not automatically be updated as new versions appear. Depending on how you see it, this might actually be an advantage. Albert is in strong development, and a new version may sometimes have issues.

The second link on the page, "Grab binary packages directly", allows you to download 64 bit or 32 bit .deb installation files.. Right-click the downloaded .deb and select "Open with software installer". This will install the .deb file using Ubuntu software.

There is no package of Albert released in the ppa:flexiondotorg/albert for 18.04 LTS, but you can download the 17.10 package manually and install it:

wget http://ppa.launchpad.net/flexiondotorg/albert/ubuntu/pool/main/a/albert/albert_0.11.1-1~ppa1.0_amd64.deb

sudo apt install ./albert_0.11.1-1~ppa1.0_amd64.deb

Note: I have wrote message to @flexiondotorg to get package for 18.04 LTS in near future.