A installation-guide for Ubuntu 18.04 Bionic Beaver is missing on
https://www.playonlinux.com/de/download.html
wget -q "http://deb.playonlinux.com/public.gpg" -O- | sudo apt-key add -
sudo wget http://deb.playonlinux.com/playonlinux_bionic.list -O /etc/apt/sources.list.d/playonlinux.list
sudo apt update
sudo apt install playonlinux
Worked for me... but didn't install wine-stable or xterm as a dependecy. Anyways, adding the guide would have helped me to install the latest version faster.