Ubuntu Nextcloud Desktop Client Update Failes

I have installed an Ubuntu system version 18.04. I have installed the NC desktop client version 2.3.3. it tells me every day, I should update to client version 2.6. I let have ran in Terminal:

$ sudo add-apt-repository ppa:nextcloud-devs/client
$ sudo apt-get update && sudo apt-get upgrade

But nevertheless, I have only the client version 2.3.3.

What am I doing wrong?